You will be able to select between Premium or Basic battles in the new Battle screen, which is on your home Menu alongside the Shop and your Pokémon. You can enter the Premium battles in exchange for a Premium Raid Pass, and it offers better rewards - as long as you win.
You'll be matched against random players online, and luckily, the community is very active, so you shouldn't struggle to find players. Right now you can only enter Great League battles online, meaning your Pokémon can have a CP no higher than 1500. Make sure you get some strong mons just below that CP level before you go in.
Luckily, even when your Pokémon get injured or faint in this mode, you won't need to use your Revives and Potions on them afterwards in order to get them up to fighting form again.
Type effectiveness and attack speed
One of the most important strategies you can put in place is also one of the most basic and obvious: type advantages. You won't be able to know what three Pokémon the enemy is coming into battle with, but you can try and ensure you have a balanced, strong team to take them down.
Normal types like Snorlax and Blissey, for example, have high HP, and can be problematic. Which is why you should come armed with a Pokémon with Fighting type moves to take them apart quickly and easily.
Pokémon with higher attack speed will also be handy and can charge their strong attack more quickly, but there is no easy way to see your Pokémon attack speed in-game, you need Google for that…
When you're up against a Pokémon with a type advantage against you, it's time to swap out, but that can cause it's own issues.
Swapping Pokémon will reset your charged attack, which of course, is the best way to do damage. But not only that, you will be set with a long swap timer wait until you can change Pokémon again, which can come back to bite you.
Though of course, if you see the opponent swapping Pokémon out, you can use this to your advantage, because you know they'll be locked into using that Pokémon for a period of time.
As long as you win, you can get big rewards from battling trainers online, especially from the Premium route, and that is most certainly the main reason to go into these battles.
The only thing you should keep in mind is that after battling against other trainers, you will have to walk for 5km before being able to battle online again. This, if nothing else, is a nice way for the game to ensure you never neglect any one aspect of the game.
But if you want Rare Candy, Sinnoh Stones, and many more items, you should definitely get battling as soon as you can.