@Sunisshiningandsoareyou
start by picking out one that you want to do. It should come with everything you need to start. I bought a carry bag that has little containers to store the diamonds in. There are paintings with square diamonds or round diamonds. I just ordered my first one with square diamonds! If you enjoy it, there are tons of accessories you can get on Amazon. I even have a tote bag to carry my stuff in when I go to my sisters or best friends house. You can also get pens that light up. But I would try one painting first before you invest in a bunch of stuff. The only think you will need is a Diamond painting sealer.
I always start in the bottom right corner so my hand/arm don’t stick to the painting. The biggest tip I have is to label your diamonds and keep them organized because there are thousands of them and if you get them scattered it’s a pain!