If you want to integrate properly with WordPress consider using Custom Post Types instead of creating tables in the database.
In your case you could have two new post types:
Events
Event participants
Here you can find more information about custom post types:
https://codex.wordpress.org/Post_Types#Custom_Post_Types
This site is handy for generating the initial code that facilitates your new post type:
https://generatewp.com/post-type/
Alternatively if you’re not comfortable with coding it you could try searching for an events registration plugin.