I dunno how sex works

Me

Okay so. I’m a teen female. And I’m not used to the whole concept around safe sex and how much I should trust the iud. Should I stop worrying so much about pregnancy and trust it or what? Is there still a chance of pregnancy if he never comes ( reasons of our own)? Can anyone tell me how I should look at my sex life? I have no idea how to approach things since I’m worried about pregnancy. Please help!!!