Calling all spacemen!! I need help!

Ok so I think I have finally realized that I may be a little mentally retarded. My family has always said I am a little slow but I have never wanted to believe them. Today I have realized it for myself that I actually am. My reason for thinking this is...

I AM NOT A COMPUTER SAVVY PERSON!!!!!

Did you get that? So I have been trying to make my blog more cute by putting some cute touches on it, but everything I try to do for it never turns out right. First of all I have tried to put some backgrounds on it but the backgrounds seem to all be too big for my page and I don't understand why. Like half the background is cut off. It is so annoying because the part that is cut off is the cute part of the background. Does anyone have any idea why that would be? If they do I would love to know why so I can fix it.

My second thing that I have been trying to do is put a banner up on my blog so that I can have pictures on it but no matter what I do, I can not get the banner to work out. I have tried putting pictures on it through multiple programs and I cant get any of them to work. AHHH this is driving me up the wall! If you know an easy way to get this done please leave a step by step instruction for this slow mind of mine so that I can make this blog cute. Like I said I am not computer savvy. I hope someone can help me. I am so desparate. :}