Header and Theme HELP

Ok, so thankfully I was able to resolve a problem earlier today. Now, I’m trying to figure out to put in a personal header on my site. I’ve read, I’ve download ftp clients and I can’t seem to figure it out. I have a Mac if that is any help. But I want to change the color, links, font color as well. It just is all very confusing. And this all that I kind of need to do. Please, thank you.