In soccer referees carry a standard to signal calls. It is almost like sign language so signaling properly is important so as to carry the correct meaning on calls.
Below are some great links to proper signaling for a center referee:The KickoffOffside/Indirect KickGoal kickCalling in a substitute playerSignaling end of half Signaling a score occurred
PenaltyCorner kickCenter ref signaling a throw inAdvantageFree KickStopping play for injuryWarningStopping play for injuryCalling in for medical aidIssuing a cardDowngrading a cardCLICK
HERE FOR A GENERAL GUIDE FOR CENTER REFEREE SIGNALS AND BODY LANGUAGE.
Below are some signals for the Assistant Referee:
Goal KickThrow inIncorrect throw inSignaling a scoreGoal kickmovement after a scoreOffsideBall out of playCorner kickFree kickSubstitutionProper way to switch hands with the flagCLICK
HERE FOR A GENERAL SUMMARY FOR ASSISTANT REFEREE SIGNALS.
Of course the best approach is to see them working both in unison on the pitch. Here is a fabulous
link to the center and the AR in a combined signal guide.