What are SIDS and STARs?
Both are predefined routes through the air which connect the airport areas (terminal areas) to the enroute airway system in a way remotely similar to local roads that everyone follows from and to highways. This ensures (in theory) an orderly fashion of after departure reaching (SID) and leaving towards the airport (STAR) the enroute airspaces for all aircraft.

SID stands for Standard Instrument Departure.

STAR stands for Standard Terminal Arrival Route.

The links touch upon everything else.