Trouble Getting Started

Maybe I am in over my head. But I am a fast learner and would greatly appreciate some help. I have a Mac OS X, Version 10.4.3. I am starting up a blog for my mom’s small business. The host site I chose is “hostgator” and obviously “wordpress” is helping me craft the blog.

I cannot figure out where to upload files, I can’t find the wp-content/themes/default folder. I do not see where I can move files around on wordpress. The zip files are confusing- where do I put them?! I have read over the How-To’s… and still do not get it. Changing the theme has proven impossible for me, yet it seems like it should be so simple. I’m a mess. Please help. Thank you kindly.