I finally opened my account with BlueHost!

But now I've already got sort of a technical question about setting up additional sites.
I plan on creating a series different sites on different health topics, assigning each to their own subdomain on my single domain name. I figure this way I can avoid buying a whole string of separate domain names.
My question is, which is the better way to handle this? Should I refer to them as subdomains, such as: subject.website.com, or should I use folder names, such as: website.com/subject?
I've created one subdomain on BlueHost so far, and it seems to be accessed just as well whether you type it in as a subdomain or as a folder, so I'm a little confused now. I'm worried that it might be much better SEO wise to do this one way or the other.
Any advice? Seaching around elswhere on the web only got me more confused. Thanks in advance!
P.S. - Thanks again to Holly for your help in getting my template set up, even though I had to go and choose a little of a problem one!