Highschool girl's soccer!?

you need to know the time for each half, the time runs up for instance if its a 30 minute half, it runs up from 0:00 to 25:42(example-25:42 has no significance) and ends at 30:00. the time never stops when the ball is out of play or a foul is called. the ref may add time after the half for stoppages, add 1 goal when the ball crosses the line between the upright posts and under the crossbar, and the ref points to the middle and play is resumed from a kickoff ..

well that's the basic stuff also, in the second half time usually starts from 30:00 and ends at 60:00

it may not it's different in some places time may run down from 30:00 to 00:00

ask a ref

If you are working the scoreboard all you have to do is put the score up every time a goal is scored. The game is 90 minutes, 45 minutes per half, but don't worry about keeping time, the referee is the only person that keeps time. He will blow his whistle when time is up so a time clock means nothing.