The truth is that there is no trick to slot machines. They provide random results based on set mechanics and it all comes down to luck. With that being said, not all games are the same, so picking the right options is key, and you can still change the size of the bet throughout the session for better results.
If the odds offered on a particular selection are -110, that means in order to 'win' (profit)R$100, you would need to wagerR$110. If the odds are +110, it means that if you wageredR$100, you would 'win' (profit)R$110.
The odds for favorites are accompanied by a minus (-) sign and indicate the amount you need to stake to winR$100. On the other hand, the odds for the underdogs are accompanied by a positive (+) sign and indicate the amount won for everyR$100 staked.