Here are some of my favorite directions for sewing cloth prefold diapers.
How to make a prefold diaper from T-shirts and scraps
How to make a prefold diaper from one T-shirt
How to make a 10-minute prefold
How to make a prefold with two large pieces of fabric
How to make a prefold the "real way"
I have used the top one most; it is the pattern I used to make the diapers in the photo. I have also used the second pattern and really like it. I have two diapers made from the third pattern and I recommend using a stretchy fabric with it and with the fourth.
There are other patterns on the Internet; just search "sew cloth diapers" or something like that and you will find lots of links. These links I have posted here use mostly recycled materials like old clothing since that is how I like to make my diapers but there are many other patterns with other fabric choices out there.