If you can, you pin the string on the table. If not but you have somebody to help you, let the helper hold the string instead of the pins. If you work alone, pin them to the knee of your jeans, first the safety pin through your jeans, than through the string at the place of the pins, than through your jeans again.
Start now with square knots with the strings around the loop. If you do not remember how to make it, click on the picture of the square knot at the end of this text.

Go on till your strings are nearly gone or till the loop gets the right size. Pull every knot tight and when you get to the end of the row pull on the loop while holding the last knot. If you do knot want more loop, (because the length of the loop is just right and the string all used, do not pull or not as hard.)

For the one variation I did not do any thing but using two colours of string.
The other variation is even simpler to make. I used again two colours of string but besides I used the turning square knot. Here you do tie the knot every time from the same side. If you click on the picture of the turning square knot, or that the other way round, you see what to do.