Hi, I am making an Application on Ionic 2/3 in which you can track your friends, you can chat with them, share your route etc.
My problem is that i don’t know where to start from ?
Do someone knows about this ? How to start plan or start developing it ? Could firebase be use for chat application ?
Thank You 
Start with the features you want and design from there. You should choose a design that you think would give the best user experience.
I have no idea if firebase could support a chat application. I bet it probably could but any database you use will probably get expensive fast based on traffic.
I’d think of potential features, their practicality, design, then implement features.
If you’re a novice developer I would try a more simple tutorial first. JavaScript is one thing, Angular5 is another, and ionic also differs from Angular. If you aren’t comfortable with Angular5 (aka Angular 2) then you’re going to have a tough time.