Its quite easy:
Star spangled Banner sung
Local celeb/prize winner throws a ball
Young child on big screen says "Play Ball"
1 team bats 1 team fields
1st innings or "top of the first" starts with a batter and a pitcher "bowler" who throws ball. If batter hits it he must run unless he hits it...
Went to Safeco Field last night to watch the Mariners beat the Athletics 7-2. Lots of errors by Oakland and just one home run, scored by the Athletics. Nice old stadium with a massive retractable roof, although it wasn't needed.