Forza Horizon 4

#FORZATHON Live events are public events that trigger every hour in a certain place on the map when you're online. You need to drive to the bright pink/purple circle on the map, for which you will be informed by a notification on the top-middle part of the screen. That will also unlock:

To complete all three rounds after successfully entering the event, you need to complete three different objectives, one after the other, in cooperation with the rest of the players that are participating within a time limit. One could be a jump, the other a speed zone, or a speed trap, a drift or a skills zone, all in a random order and a random selection. Once the team completes the first objective, it moves on to the 2nd round and the event goes on. The objectives work cumulatively, as you need to pass through the speed zones or do the jump for example a few times so the team reaches the required goal, for example 2 kilometers of total distance jumped from a jump, 1500km/h for a speed trap, 100 Air skills etc. The more participants the better are your chances, but unless a lot of players go afk, you won't have an issue completing the whole event on your first try even.

You should tackle each objective like the respective challenges in the singleplayer. The slight difference is that you shouldn't be looking for perfect runs, but rather a balance between putting up numbers often and scoring big. For example, there's no point in backing off for 5 kilometers so that you can hit 380km/h on a trap. Turn around sooner and hit 310km/h. That way, you'll contribute more efficiently towards the goal and increase your chances of completing all three objectives before time's up.

Keep in mind that you can have any car delivered to you at any time, so if the car you're using seems unsuitable for a drift zone or an offroad section, don't hesitate to pause the game, go to the Cars tab, then My Cars and select another car you own. Chose "Yes" when asked whether you want that car to be delivered to you and after a loading screen you'll spawn near your last location in the selected car. You don't get kicked out of the event, so you can drive or fast-travel to the next objective to continue.

Anima Puras guide is spot on! But i made a little video just explaining the whole thing, and just general tips.
Remember, you can be as good or as bad as you want, if there are a decent number of people, the 3 achievements can be EASILY obtained.
Its a GROUP effort, so if you want to add just 1 point to the board you can! (Although try not to be that guy lol)

As for cars, try and stick to one that YOU are comfortable with. Personally, the Lambo avendator is the one for me, but whatever works well for you will be best!

I Explain the ins and outs of the achievements for the first 1.30, so 1.35 and beyond is where you see me doing the 3 rounds and explaining each one.
Thanks for watching, hopefully this helps you guys and gals out!