Themes not loading

Can someone please help me?

I just installed wordpress on bluehost. I tried to install a custom wordpress theme and its not loading at all – all I get is a clear box where I should see it. The person who made it says if it isn’t loading its because the syle.css needs to be correctly linking to the theme. I don’t know what that means or how to change it.

I tried to load one of wordpress’ themes instead for the time being but that won’t load either. All I get is a timer going round and round. So basically I can’t do anything right now.

If anyone can help please write what I should do step by step because I probably won’t understand what you’re referencing if you don’t.