If you are struggling with different versions of ruby and ruby on rails in your projects, follow this video (https://www.youtube.com/watch?v=cQVb7fHFjSM) to define the versions and also the gemset for each project. This way nothing will be messed up when switching between projects. This helped me out a lot.
OBS that the video has older versions but your terminal will tell you that and what to do. And RVM apparently does only work for mac.