A bet in this market is a bet on which player will score the first goal of the match. So simply find the guy or girl you think will score first, and have a bet on that player. If your selection scores first, your bet is a winner. Any other goalscorer, and your bet is a loser.
A word of note, different bookmakers have different rules for own goals, and if your selection doesn’t actually start the match. So make sure you are aware of the terms and conditions before you bet.