First cut into the gusset to make the neckline.

Then you cut the sleeves.Fold one leg lengthwise in half and cut. Here it's your choice how long the cuts going to be, but I recommend to make them longer than shown on the picture. Furthermore you can work with your ruler to have a nice line.

Now unfold and stretch it.
You can now leave it as it is or follow the next step.

This will be a little tricky. Begin where you shoulder will be. Take the second stripe,drag it behind and then over the first one to create a little loop. Now take the next stripe and do the same. Do this the whole sleeve along. In the end, cut the last loop in half and knot it to the previous one.

Finish!

You can also do this at the back ;)