Aquaman's journey, in order
To watch the Aquaman movies in order, start with Zack Snyder's Justice League, then Aquaman and Aquaman and the Lost Kingdom. That's 3 out so far, about 8 hours, ending with Aquaman and the Lost Kingdom.
Jason Momoa's Arthur Curry joins the Justice League before his own films make him King of Atlantis.
Updated
The Aquaman movies in order
Zack Snyder's Justice League
Batman recruits Arthur Curry.
Aquaman
Arthur claims the throne of Atlantis and meets Black Manta.
Aquaman and the Lost Kingdom
Black Manta returns, and Arthur needs his brother Orm.
Questions
What order should I watch the Aquaman movies in?
Start with Zack Snyder's Justice League, then Aquaman and Aquaman and the Lost Kingdom, and follow the list above: 3 in all, ending with Aquaman and the Lost Kingdom.
How long does it take to watch all of the Aquaman movies?
About 8 hours for the 3 out so far.
Do I need to watch Justice League before Aquaman?
No. Aquaman tells his origin on its own, but Justice League shows how he first joins the team.
Watch the Aquaman movies with Chronologica
Make a plan of just the Aquaman movies, mark them off as you go and always know what's next. No account needed.