Are other people able to see what I do on my iPhone?

sometimes i get paranoid that my friends, classmates, family, or whoever is able to see what i do on my phone. i know that probably the only big ways to do that is through parental controls or if someone hacked into my phone- and my parents can barely even use the editors in the photo app- but still.

is there a way that i can know if someone has access to see all that i do on my phone?

[Re-Titled by Moderator]