Mission Type: Build your Lineup with players from X different regions.
Explanation: Regions are the geographical term used for the LoL esports leagues worldwide, for example, the LCS is the League from the North American Region. So, if the mission is asking you to add players from '3 regions', it's asking you to pick players from '3 completely different Leagues'.
Note that Worlds has multiple teams from specific regions, and picking players from two different LCS teams, for example, will only count as players from 1 region.
How do I complete this mission?
You can complete this Mission anytime during Lineups are open for the particular week. The Mission itself will show progress once you start adding your players.
When do I get my Bytes?
You will receive your Bytes after the lineups lock for the week, this ensures you have X players from different regions going into the matches.