For the most part, movie versions of comic book properties have largely avoided the convoluted continuity that’s always been (for me) the biggest barrier to reading comic books. With the ongoing success of the MCU, however - and to a lesser extent,
Deadpool and
Batman v Superman - we’re starting to see more and more characters forming larger and larger teams.
The X-MEN franchise's ownership by Fox means that (for now) Avengers crossovers are off the table - but there have been a LOT of X-Men over the years, and
X-MEN: Apocalypse wants to play with them all.
To that end, it brings back most of the
First Class/
Days of Future Past roster (Xavier, Magneto, Mystique, Beast, Havok, Quicksilver), along with the titular Apocalypse; joining them are new versions of Cyclops, Jean Grey, Storm, Nightcrawler, and Angel, plus cinematic newcomers Psylocke, Jubilee, and
Caliban.
Most of these characters have very little to do; aside from Magento, Apocalypse's horsemen serve the same basic function as set decoration.
Jubilee's entire contribution is taking Nightcrawler to the mall.