Service is a form of delivery of any lawsuit according to the court rules. It can vary widely between states, but usually requires personal delivery at the person's residence unless the court authorizes another method of delivery.
If someone is trying to serve you with a Summons and a Complaint, they are trying to sue you. You should see if they left a number with your mother and give them a call to figure out who is trying to serve you. I would not recommend ignoring them, if you do that they may decide to serve you by publication and then you would not know who is coming after you.
You have been sued. The summons is the official notice of the suit, and provides you with information on protecting yourself. Attached to the summons is the complaint which lays out the claim against you. Generally you have 21 days to respond once you are served. If you do not respond, a default judgment will be entered against you.