Here we have a regular box full of, for demonstration purposes, random OU-legal pokémon, as seen in the teambuilder.
Wow, look at all those mons!
After matching with another player on the ladder and saying gl hf to each other, we pick a lead. Today, we're in a Quagsire kind of mood,
so we'll pick Quagsire as our lead. The remaining 23 team members
then get their team position shuffled around, and we end up with this team order (left to right, then top to bottom):
1. 2. 3. 4. 5. 6.
7. 
8. 9. 10. 11. 12.
13. 14. 15. 16. 17. 18.
19. 20. 21. 22. 23. 24.
(note: if you have a Zoroark, you also get to pick who gets priority to be in the final slot. This is counterintuitive though, for reasons we'll see later.)
But!
This is not what the player sees! After sending out Quagsire, the player looks at his team and sees this:
Barring our active Quagsire,
we can only see and freely switch between the first five pokémon in our party (our "hand").
But it looks like we won't need to do that, because our opponent sent out a Coalossal! Predicting a switch, we go for a Toxic. As predicted, the opposing Coalossal switches out, a Sceptile comes in, and we miss our Toxic.
Damn you, 95% accuracy!
This is bad. Sceptile threatens us, so we'd better switch. But when we look at our hand, we see this:
Oh no! Our Dragalge is gone! This is because
every turn, the Pokémon at the frontmost of the party (excluding the one who is currently sent out) gets sent to the back of the party, and the next in line takes its place. This happens for two reasons:
1. It is similar to "drawing a card"
2. It limits the powerful switching option to a small section of your party, instead of a constant 23 other mons.
So now, Dragalge is at the back of the invisible (to the player) line, behind Tapu Fini.
But look! The
heart of the cards has heard our prayers,
and our Clefable has appeared! Sceptile's Leaf Blade can only 4HKO our Unaware defensive clefable, so we switch to it.
After switching and taking 31.9% damage from Sceptile's Leaf Blade, we need to take note of two things:
1. Our current hand has changed once again:
(in terms of order, Tapu Lele has gone to the back of the line
before Quagsire was switched out, so Quagsire is in the last slot of the party.)
2. We just used our first "switch".
To ensure the metagame doesn't turn into a stall fest, especially with regenerator, volt switch, flip turn, etc., every player is limited to a
40-turn switch limit. On the 41st switch,
the player loses by deckout. This is similar to
losing by running out of cards in a card game.
Back to the battle. We're confident in our Clefable switch, so we decide to set up a Calm mind. But our lucky opponent
crits our Clefable with an Iron Tail, knocking it out! Really? Who runs Iron Tail Sceptile?
Something big just happened. We may have 23 mons left,
but we can only afford to lose five more. Once a player loses 6 Pokémon, he loses the game by defeat. This is similar to
losing a TCG game, by letting your opponent get six prize cards.
However, upon looking at our team, we see this:
We get to choose from all our remaining 23 mons! On some special conditions, such as fainting,
you'll be able to choose from your whole team instead of your current hand. However, when doing so,
your team will be reshuffled. Upon sending out a new Pokémon,
the fainted mon will permanently move to the back of the line, and stay there, immune to reshuffling or moving up the deck.
And... I think that should give you a good idea of how to play this meta!
avoinding a KO is always nice
Good against weather
hazards are even more dangerous in this meta
status and confusion are also omnipresent
better than destiny bond
