As you remember them
Well the first thing you might notice about gyms in 2018 is that they're, um, well they're pretty much the same as ever?
That's not to say there aren't new things however, that we'll talk about here, but when it comes to battles, taking gyms, and holding them for Pokécoins, that's all still in place.
Battling is pretty much the same. You'll have to take down opponent Pokémon three times before they relinquish the gym to you, and you can install one of your mon. One thing that has changed though, is you can spin gyms just like Pokéstops.
If you haven't played in a while then you'll likely notice that gym placements have changed around, or there are more of them.
In general the team at Niantic have been tweaking the placements of Pokéstops, gyms and other locations to make for a smoother experience for players.
Since the gyms also double as locations for raids, it'll be good for you to scout out the locations in advance, place your Pokémon in the gym, and you might even get an EX Raid Pass.
When you place a Pokémon in a gym, it's not actually at full power, sadly. You can top up your Pokémon HP though, with berries.
When not using berries to calm wild Pokémon, you can use them to restore health at gyms your mon are guarding, and you can even do this from far away.
It does mean though that you can actively thwart anyone trying to steal your gym away by healing your Pokémon as they go. Crafty!
A raid near you
Raids are multi-man events where an extremely strong Pokémon will be available for challenging, and in many cases, you'll need friends to help battle them.
Raids can be tracked using the Pokétracker in the bottom right and on the Raid tab. You can see the raid level, when it will start, if it's ongoing, and what Pokémon has appeared.
You'll do battle similar to gyms, by tapping away and swiping left and right to avoid special attacks.
Once the Pokémon is defeated, you'll get special balls based on how much you helped, and then you can use those to catch the Pokémon you fought. Use a Razz berry of a Golden Razz to calm stronger Pokémon down!
One man army
Raids are, as we've said, meant for multiple people to take on, but that doesn't mean you're unable to challenge them by yourself.
In fact, as long as you've got a couple of Pokémon with around 2,000 CP, you'll be able to take down a level one raid with little issue by yourself. A level two raid is doable, but much more challenging.
Level three, four, and five raids, though? That's a different matter. The Pokémon there are much more challenging, so perhaps go for a walk with a friend who's prepared to take down some raids alongside you.