If you wish to block a user, you can do this by visiting the users profile.

Once you are on the users profile, select the icon in the top right corner.

This will then present you with a menu which has the option to block the user.

Once you have blocked a user, you will no longer see their profile, any of their posts or any comments they leave on others posts.

They also won't be able to see your profile, any of your posts or any comments you leave on posts.