my question: while WHAT is True?

While True is True.

The while loop will run as long as the conditional expression evaluates to True.

Since True always evaluates to True, the loop will run indefinitely, until something within the loop returns or breaks.

You aren't changing the value of intb after you have rejected its current value. You need to repeat the call to input inside the loop.

inta=int(input("enter the first number"))
intb=input('enter + for addition, - for subtraction, * for product')
intc=int(input("enter your second number"))

while True:

    if intb == '+' :
        print(inta+intc)
        break
    if intb == '-' :
        print(inta-intc)
        break
    if intb == '*' :
        print(inta*intc)
        break
    else:
        print("error try again")
        tb=input('enter + for addition, - for subtraction, * for product')

You'll probably want separate loops for each input, to accommodate non-integer inputs for the operands. Once the values of inta, intb, and intc are confirmed valid, then you can do the requested operation.