For new players the Portals can be seen floating in the midst of Evil Fog. They appear greyed-out and shrouded in mist, with a bar stating how much Dragon Power you need to unlock a certain Event on top of them. Tapping any Portal brings up the Event's description.
Once you get past the required Dragon Power threshold and unlock the specific Event, the Portal moves to the bottom left side of the Camp. Tapping it either brings up the Event Rewards window, or informs you that there's no Event happening currently.
This Portal floats in the upper right part of Evil Fog clouds. Once you unlock out-of-Camp Events (not including Den Events) it moves to the bottom left side of the Camp. To unlock out-of-Camp Events you need at least 100 Dragon Power.
Event Portal Upgrade
Starting from the 1st of June 2021 some players received an ability to upgrade their Event Portal to improve Event Rewards. On the 1st of October 2021 the feature was rolled out to a larger set of users, but it's still in Beta and not available to everyone.
Note: For more information please check the following reddit posts: thread collecting all upgrade quests, threads showing how some versions of upgraded Portal affect Event Rewards and Roulette spin after Events. Please note that the feature is still in its testing phase and gets updates and changes frequently.
Camp & Chill Portal
This Portal floats in the upper left part of Evil Fog clouds. Once you unlock Camp & Chill Event it moves to the bottom left side of the Camp, below the Event Portal. To unlock Camp & Chill Events you need at least 250 Dragon Power.
This Portal floats in the middle top part of Evil Fog clouds. Once you unlock Seasons it moves to the bottom left side of the Camp, above the Event Portal. To unlock Seasons you need at least 300 Dragon Power.