Each Profile, aside from your personal one, will have a Post Options button. Once you open the menu, you'll have an option called I Don't Like This, which, if accessed will give you a few options. The two you're looking for are "Not Interested in the topic" And "Block".
Not Interested in the topic - will block the topic from showing up on your Newsfeed
Block - will block the profile that created the post
You can also block a profile directly by going to Profile you want to block, hitting the three-dotted button to open the profile's options, and choose Block
Blocking someone will stop them from interacting with you directly, as well as stop them from finding you in Search Results. They won't be able to Follow you or to write to you via Chat. You will still be able to see each other, in cases in which you both follow the same Topic.
Topics are public spaces that we don't interfere with. They won't be able to contact you, but they can Like and Tip your posts if they encounter you on a Topic.