I pulled out some of my hair. Will they grow back or do I need to do something else?

They should grow back just fine. Repeated plucking/pulling can cause damage to the grafts over time but as long as there is no physical signs of damage like blood etc. the hair should grow back at a normal rate.

There are a lot of variables to this question.
If this is a persistent problem that involves repetition or follicle damage it may be difficult to have regrowth. If you accidentally pulled some hair out and are in good health, your hair should grow back just fine.
Your family doctor or dermatologist can take a look at your scalp and help you to determine the scope of concern. 

Provided there was not much inflammation associated with the hair pulling, and it was a one time event, it likely will grow back. If the pulling is chronic (ongoing) or if the pulling was associated with inflammation, bleeding, etc (severe) - it may or may not come back. Please see a dermatologist if concerned.