If it's your first time contributing to open source
For selecting an issue:
I totally don't know what I want to work on => start with writing tests
I have never done any of this before => start with writing tests
I have something that's bugging me and I will personally fix it myself => see if it's within known issue, and either personally talk with ms boba about how hard it would be to get it done or open a new issue to discuss it
I have a feature proposal that I want to implement => no idea what the process is, but if it's big first do other stuff around the codebase and then we'll discuss it
I don't know what I want to do, but I know I want to learn how to do X => talk with ms boba and she'll help you figure out the right fit