In order to start knitting you will need to get that first row of stitches onto your needle. There are several different methods of “Casting On” and no matter which one you decide to learn you will need to start with a basic slip knot.
To create a slip knot you start by folding a bit of yarn and twisting it to make a circular shape. Depending on what type of cast on method you are using you will need a different length of yarn tail. Refer to those tutorials for more info.
Then you reach into the circle and grab the tail of yarn that is on the bottom of the twist. In this case the green bit is laying under the orange side… so I grabbed the green yarn.
Pull the yarn up through the original circle. It will create a lasso looking knot.
Slip this knot over the end of your knitting needle.
Tighten by pulling down on the tail of the yarn.