The events run for a limited time and in this time, you can play as much as you want (PvP) or until you complete all races (PvE). The absolute condition to be able to see any active event is: beat boss 4 in the respective tier to be able to see PvE event, and beat boss 5 in the respective tier to be able to see PvP event.

The entry criteria in each event will be different from event to event, sometimes we have events with free entry cost, sometimes it can cost gold and/or requires a certain car model/manufacturer. 

Please check the entry criteria on the event via the map.

PvE event is when you play a certain number of races (as many as chosen to setup, but usually 20 races) and you play against AI. Each race has a different reward, and there is no final reward for completing the entire event. It's like the normal ladder in a tier, but with much better rewards, which is why we call it a ladder event. This is also where we set stage 6 resources, customisations and fusion credits as rewards.

PvE, you get rewards at the end of the race

PvP is when you play as much as you want against other player's ghost (or if no ghost is available for you, you're matched against an AI). There isn't a number of races, but we do cycle between 5 different tracks. You only have 1 opponent, as opposed to PvE where you have 5.

PvP, you get the rewards when the event finishes