If you'd like to post on a blog, open the blog and scroll to the Reply box at the bottom.

If you'd like to post on a thread, open the thread and do the same.

If you'd like to comment on a guide, click the Discussion tab and scroll to the box at the bottom.

Hmm?

All you have to do is click the big Forums & Blogs button at the top, and then you go to wherever you want to make a post ^^