[Martijn]

Thank you very much I really appreciate your response. I've downloaded the code and built it and now trying to see my way through it.

So You're saying I should just find an unclaimed issue and work on it?

 Correct, just anything you want to work on. There's also a backlog on https://trac.kodi.tv/ (which can be viewed if you use the forum account to log in). Be sure to only look at issues created for v18 or confirmed to be an issue. 
Another topic we could use help on is cleaning up the code in general or doing improvements.
Inside the code you will also find "todo"  items that might be nice to get picked up to get yourself familiar with the code https://codedocs.xyz/xbmc/xbmc/todo.html

If not certain how to handle something be sure to ask before spending too much time on it and i'm sure one of the devs will point you in the right direction. Once that is done you can create a pull request on github for code review