First you make a chain, then you stitch into each chain link. It is a little awkward at first but the more you crochet the more "fabric" you have to hang onto. Try a dishcloth, its square and not complicated.
Use a size J hook and chain 15. Sc into each chain, turn your work. Chain 1, Sc across. Repeat until its the size you want.
I'm left-handed too, and like making granny squares. That starts with a chain that you join to form a ring, then you crochet into the ring.
If you look at a starting chain link you see it has 3 parts. The top of the chain, the bottom of the chain, and the back of the chain.
Do not twist the chain when working, always keep it straight. You hold onto it with your right hand, I think I use my thumb and forefinger to hold my work.
Insert the crochet hook into the top of the chain link to make a stitch, unless the pattern says to insert into the back of the chain link.
Also, try to keep your tension the same. If the chains are too small, loosen your tension. After awhile you will find your working gauge, whatever is comfortable for you.
Keep practicing and if you have any questions post here or send me a private message!
Lois