I don't want a particular person to see or comment on my Instagram posts, how can I block them?
Instagram offers several privacy settings that allow you to avoid specific people. You can block people by opening up the app on your iPhone and tapping on the target user name to bring you to their profile. Then tap the "..." button in the top right and select "Block." Verify that you want to block them and tap Block again.
Now they will be blocked from viewing your profile, story and posts, and Instagram will not notify them that you blocked them. Aside from blocking people, you can also make your account private and remove followers.