To earn this achievement, a player simply needs to complete the objectives requested by one of the active "weekly" challenges in matchmaking. Currently, out of the 10 weekly challenges randomly assigned to each player only 3 are active and thus are the only ones that can be completed in their next multiplayer match. Players who have purchased the season pass will have 4 challenges active at one time. Weekly challenges reset on Tuesday at 18:00 UTC.
NOTE: When a limited time event pass is offered, 10 of the "weekly" challenges become "event" challenges. These challenges do NOT count for the purpose of this achievement and will unlock the "Limited Addition" instead:
Since Halo Infinite lowered the amount of weekly challenges from 20 to 10 weekly after Season 2, this achievement temporarily becomes unobtainable when an event pass is running.
The weekly challenges each player gets is 100% RNG and vary from person to person. Challenge swaps are available if the player wishes to replace one they find undesirable or difficult, however usually the first challenges in a players stack tend to be simple and easy to complete.
Bot Bootcamp qualifies as matchmaking and many challenges that don't include the "in PVP" qualifier can be earned in that playlist. It should be noted, due to poor QA in some of the challenge descriptions you may find some challenges that should work in Bot Bootcamp occasionally don't and vice versa.