Somewhere on the left of your screen is a little menu tab, like this:

Swipe it to pull out the Amino menu. Part way down the menu, you'll see our categories.

These exist like a filing system. You can browse a category to (hopefully) find posts on topics you're looking for. When you're making a new post, be it a blog, a poll, or whatever, you should assign it to 1 or 2 categories to make it easier to find.

Nobody scrolls through page after page on the recent posts feed to find something posted 2 months ago, but they might still look at your 2 month old post if they're viewing a category.

While editing your post, tap the categories button:

Tap the 1 or 2 categories your post belongs in, and then tap the check mark at the top to save your categories.

Your post will now show up in the category(ies) you picked!

Warning: don't spam! Only pick categories that suit your post. Talking about your new channel? Pick "Channel ments." Making a post about your latest art video? Pick "Art & Animations."