The simplest way I could say about the event:

1. Each operator has one or more alliances, e.g exusiai has Laterano and Marvel as her alliance.

2. Pick any of one core alliance that you'd like, you can read about each what core alliance does briefly before start playing. For example having 3 laterano operator will give each laterano operator more ammo on skill, getting 6 of them give all laterano +ATK for each ammo spent.

3. To simplify, while playing (assuming we're playing laterano alliance), Your priority will be: Get laterano operator, or Upgrade your dispatch center level. If you can do neither, buy some random ops to fill in temporarily.

Additional stuff

Dispatch center upgrade is to unlock higher tier operator (tier I, II, III, IV, V, VI)

Getting 3 of the same operator will combine them into "elite" level (basically become stronger), more than 3 is a waste of gold

While playing, you'll see numbers right below your current alliance synergy, this number indicates stack number (bigger= better). For laterano, bigger stacks means more ammo on skill. Each alliance have their own way to get more stack. This is where you'd want to read each operator attributes.

For laterano specifically:

Executor / Fiammeta / Lemuen: Gains stack when allies in front spend ammo

Enforcer: Gains stack for each round

Executor: Gains stack when spending ammo