Every Deadpool movie in order
To watch the Deadpool movies in order, start with Deadpool, then Deadpool 2 and Deadpool & Wolverine. That's 3 out so far, about 6 hours, ending with Deadpool & Wolverine.
Ryan Reynolds' Deadpool has three films of his own, and the third brings him into the MCU with Wolverine.
Updated
The Deadpool movies in order
Deadpool
Wade Wilson becomes Deadpool and goes after the man who did it.
Deadpool 2
Deadpool forms X-Force to protect a young mutant from Cable.
Deadpool & Wolverine
The TVA comes for Deadpool, and he needs a Wolverine.
Also worth watching
X-Men Origins: Wolverine
Ryan Reynolds' first, very different, Deadpool, which Deadpool mocks.
Questions
What order should I watch the Deadpool movies in?
Start with Deadpool, then Deadpool 2 and Deadpool & Wolverine, and follow the list above: 3 in all, ending with Deadpool & Wolverine.
How long does it take to watch all of the Deadpool movies?
About 6 hours for the 3 out so far.
Do I need to watch other X-Men films before Deadpool?
No. The Deadpool films work on their own, though Deadpool & Wolverine has more jokes if you've seen Logan.
Watch the Deadpool movies with Chronologica
Make a plan of just the Deadpool movies, mark them off as you go and always know what's next. No account needed.