Events-Users Database Design
An "Event" has a Creator ("users can create an Event"), Members (those who have "Joined" and not "Left" the event) and a Location.

You should have the entity Event with EventID, Creator, other fields such as Location, description, category, date created (optionally) Represented as an Event table with EventID, CreatorID (foreign key to Users table), maybe other fields as needed.

Then have a table EventUser or similar, which is a "bridge" table between Event and User. Field names EventID, UserID which keeps track of users registered to the particular event.

User table is self explanatory with UserID plus whatever other fields are needed for the user.

Do you need to keep track of the "history" of created/deleted event, joined/left event? Then add appropriate tables accordingly and ensure the event is updated accordingly. e.g. add an entry to a table saying that a User was added or deleted to the particular event. You could do this via the business logic in the application itself, or perhaps with an update/insert trigger.

Presumably only the Creator of an event can change details such as the date and location, so you will need to take that into account in the way your application updates these.