The best way to find it is to warm yourself up first. It's easier to find if you're aroused. It's not really a "spot" but more of an area. Everyone is different though, some don't have to go in very far and others have to go in rather deep. When you're really aroused take a finger or two and insert them into your vagina. Curl your fingers towards your bellybutton gently and if you're aroused you should feel an area that feels kind of "swollen". When pressure is put on the part that feels swollen it feels spongy.
I had looked before and from everything else I heard I figured I just couldn't find mine. I read that it was going to be kind of round like a quarter and rough in texture. In my exploring I felt the area described as swollen but it wasn't really round in shape and was actually much smoother than the rest of my vagina.
Just remember to relax and don't stress. Keep in mind that it's not the "spot" people usually talk about but rather an area. Everyone is different! Texture, shape, size, and depth is all going to vary.