No worries. There is no such thing as a stupid question. If a user has enabled the ability for people to comment on their blog entries, you will see a comment box directly below the entry. See this example. A lot of users don't have this feature enabled (I believe it defaults to be disabled), so that probably makes it seem like it's not possible to comment on them.
I'm pretty sure you have to be a full member to comment on blogs and photos, as well. That might be why it's not possible for you to do so.
How can we read blogs? I've tried clicking on a few of them, and the says I don't have permission. Do you have to be friends first? Can I write a blog as a regular member?
Click on Blogs at the top, right under the EC header and next to "My Settings." From there you can go to Best Blogs, Recent Entries, etc. These will be visible blogs. If you've been clicking on links to specific blogs (beneath someone's username in a post for example), these people might have only enabled people on their contact list to view their blog. And yeah, you can write a blog as a regular member. Again, click on Blogs at the top, then Your Blog.