To execute an arbitrage bet, the bettor must compare odds across multiple bookmakers and calculate the potential profits.
The most straightforward example I can provide is the following:
Team A (the underdog) is priced at +140, which means per every $100 you bet, you profit $140.
Team B (the favorite) is priced at -135, which means to win $100, you need to wager $135.
So lets say, in this example, you place $100 on Team A to win $140.
And you then put $138 on Team B, the favorite in this case, which will payout a profit of of $102.
Therefore, in total you have placed $238 in wagered money.
If Team A wins, total payout is $240, which means you profit $2.
If Team B wins, total payout is $240, which means you still profit $2.
Regardless of the outcome, you win $2 either way.
Now to illustrate scale, let's say your wager was $1000 for Team A, $1380 for Team B, payout for Team A winning is $2400, where payout for Team B winning is $2402. You placed a total of $2,380. If Team A wins you win $20, if Team B wins you win $22. And essentially, Arb because it's as close to risk free as you can get.