What's a new workflow for a new project and shared runners?

I’ve just found that new projects don’t belong to any runners anymore even runners are shared. How to make it work? Should I everytime assign runner to a new project?

I do not have an answer because I am completely new to GitLab. But maybe someone could enlighten me about what any GitLab CI workflow is.

I have created https://gitlab.com/openmono/test for testing GitLab features. I am trying to run everything directly from GitLab.com, and have turned on GitLab CI in the project settings, selected to use shared runners, but nothing happens when I push to the repo.

Do I have to create my own runner on my own machine?