Documentation can be found e.g. at MDN. Note that .split() is not a jQuery method, but a native string method.

If you use .split() on a string, then you get an array back with the substrings:

var str = 'something -- something_else';
var substr = str.split(' -- ');
// substr[0] contains "something"
// substr[1] contains "something_else"

If this value is in some field you could also do:

tRow.append($('<td>').text(=txtEntry2]').val().split(' -- ')[0])));

There are several functions in JavaScript which can be used to split a string.

1. Split - (Split a string into an array of substrings)

var str = "This is a string";

var str = "This is a string";
    var res = str.split(" ");
    console.log(res);

It is important that split gives back an array with the string chunks.

2. Substr - (Extract parts of a string)

    var str = "This is a string";
    var res = str.substr(1, 4);
    console.log(res);

3. Substring - (Extract characters from a string)

    var str = "This is a string";
    var res = str.substring(1, 4);
    console.log(res);

Reference

W3Schools Split
W3Schools Substr
W3Schools Substring