Using Tags and Categories for your Blog Posts is an excellent way to automatically archive your blog’s content. It also lets readers access older posts. And its a good way to help Google understand what your site is about.
I find Categories to be more useful than Tags but no reason why you can’t use both. Once you learn how to set up your Categories you’ll know how to do Tags.
One reason Categories are more useful is that you can create Sub Categories. You can’t do that with Tags.
A best practice is to assign at least one Category to each post and to never leave a post as Uncategorized.