1. Put these items in an array. var array = ["Horse", "Pig", "Dog", "Cat", "Parrot", "Iguana"];
2. Generate a random number. var randInt = randomGenerator(0, array.length - 1); ( Generating random whole numbers in JavaScript in a specific range? )
3. Use the random number to get an item from the array. var item = array[randInt];
4. Use document.getElementById to get the textbox you want, and use .value = to set the textbox's value. var textbox = document.getElementById("textbox_id").value = randInt;

The DOM API you are looking for is: getElementsByClassName

onclick needs to be a function that will be called on click event. What you are doing is calling innerHTML='zufall' immediately, returning the string 'zufall', and assigning onclick='zufall', which is not what you want.

JavaScript array literals are denoted with [] not ().

I'm assuming the string 'zufall' is not what you want, but the variable zufall, which I've adjusted by removing the single quotes.

Math.random() (not random()) returns a random number from 0 to 1. Multiply that by the length and then floor to integer (You could use Math.trunc() also). And then in brackets to access that index in Orte.

Again, variables are set when they are assigned. Which is probably not what you want here. The same thing happens in Python. zufall would be assigned a value that doesn't change unless something is called to update it. This is a common mistake, although as an experienced Python programmer you should not be making this mistake anymore.
I've adjusted it so it updates zufall on every click. As you should be able to see, a global variable is unnecessary. You can just generate the zufall only in the onclick handler.

var Orte = ['a', 'b', 'c']
var zufall = Orte[Math.random()*Orte.length | 0]
button1.onclick = function(){
  zufall = Orte[Math.random()*Orte.length | 0]
  document.getElementsByClassName('text')[0].innerHTML = zufall
}

<div class="text"></div>
<button id="button1">click</button>

Use:

var things = ['Rock', 'Paper', 'Scissor'];
var thing = things[Math.floor(Math.random()*things.length)];
alert('The computer chose:' + thing);

Demonstration

Just to precisely answer your question, supposing you really want to keep your three global variables, you could do this:

var c = "Rock";
var d = "Paper";
var e = "Scissors";
var thing = window['cde'.charAt(Math.floor(Math.random()*3))];
document.write('The computer chose: ' + thing);

Demonstration

(But don't.)

If you want to grab N items randomly from an array, a classical way of doing it is to :

1. randomly shuffle your array,
2. pick up the N first items of the suffled array

Example code :

function samples(items, number){
    items.sort(function() {return 0.5 - Math.random()});
    return items.slice(0, number);
}

Notice that the shuffle algorithm is probably not the best one, it is provided as an example, as mentioned by @Phylogenesis.

If you prefer to avoid reinvent wheels, you can also use undercore.js for example, that provides a sample method

Here is an example on jsfiddle

var words = ["monitor", "program", "application", "keyboard", "javascript", "gaming", "network"];

var word = words[Math.floor(Math.random() * words.length)];

console.log(word);

document.getElementById("word").textContent = word;

And to have it fit in directly with you present code:

var getRandomWord = function () {
    return words[Math.floor(Math.random() * words.length)];
};

I'm going to assume you meant you wanted to generate a random quote and not just one word.

Here's the answer:

const motivation = [{
        quote: "Planting popcorn does not produce more popcorn",
        person: "Farmer Ted"
    }, {
        quote: "White whale, bad whale",
        person: "Confucious (Moby Dick)"
    }, {
        quote: "Use the strobe function to disorientate your attacker",
        person: "Flashlight"
    }, {
        quote: "Apply liberally to your erogenous zones",
        person: "Spice Bomb"
    }, {
        quote: "Help me, I'm bleaching",
        person: "The Great Barrier Reef"
}];

const randomNumber = Math.floor(Math.random() * motivation.length);

console.log(motivation[randomNumber]);

const generate_quote = () => {
  const quote = motivation[randomNumber].quote;
    document.getElementById("random_quote").innerHTML = quote;
}

<p id="random_quote">The random quote will appear here.</p>

<button onclick="generate_quote()">Generate random quote</button>

These are a few things you need to follow.

1. Never use document.write().
2. Don't self close <div /> tags.
3. Use event listeners.
4. Use the scoping correctly. Remove the var here.
5. Use the parameters wisely. You don't need the parameter here, which makes the global variable, a local one and you aren't passing the value too.

You aren't clear where to show the words. So, I assumed that you wanna show it in the <input />.

words = [
  'Hello',
  'No',
  'Hi',
  'Banana',
  'Apple'
];

function randomWord() {
  document.getElementById("textbox").value = words[Math.floor(Math.random() * words.length)];
}

* {font-family: 'Segoe UI';}

<form name="f1">
  <input type="text" value="" name="textbox" id="textbox" />
  <input type="button" value="show" onclick="randomWord()" />
  <br/>
</form>
<div id="new"></div>

As mentioned in my comment, store the quotes in an array, then add a click handler that selects at random from that array.

Give your button an id, so it can easily be selected from JS:

<button id="changeQuote">Change Quote</button>

Then something like this, using the Math.random() method:

var quotes = [
      "The quick brown fox jumps over the lazy dog.",
      "Look out! There are llamas!",
      "No, really, don't get up.",
      "Whatever",
      "Etc."    
    ];

document.getElementById("changeQuote").addEventListener("click", function() {
    var q = quotes[ Math.floor( Math.random() * quotes.length ) ];
    document.getElementById("test").innerHTML = q;     
});

Demo: http://jsfiddle.net/9pqqmnrs/

Further reading:

• Math.random()
• Math.floor()
• .addEventListener()

It does depend on how the list is "made".

If the list can be made by the programmer (thus static and not be altered by the user), you could do the following (copy and paste this into a .html file):

<html>
  <button onclick="randomizeFunction()">Randomize!!</button>
  
  <p>Random generated word is:</p>
  <p id="randomWord"></p>
</html>

<script>
const myList = ["List item 1", "List item 2", "List item 3", "List item 4", "List item 5"];

randomizeFunction()

function randomizeFunction() {
    document.getElementById("randomWord").innerHTML = myList[Math.floor(Math.random() * myList.length)]
}
</script>

Do note, this uses JavaScript as well! Most responsive websites are driven by it nowadays.

Javascript is the part between the script tags. For you to customize, change the items in const myList, between the [ ... ]. Make sure the [ ... ] stay and seperate items with a comma. Also, if you are to use words, make sure to quote them (making them strings), like I did.

By the way, most people don't mind to get their hands dirty and providing you with an example ('write the whole thing').

Keep going, programming is awesome!