There are two main types of call pickup:
Call pickup allows you to answer a call from any ringing phone that has the same call group as your phone. If more than one phone is ringing, you would have no control over which call you answered.
NOTE: If more extensions inside Call group 1 were ringing, you would have no influence over which one of them would be picked up.
Directed pickup allows you to pick up a call from a specific extension by dialing '*88 + EXTENSION' . For this to work, your extensions doesn't have to be assigned to any call group/pickup group.