It's best to start in Project. You can export data to Excel by going File | Save As and selecting Excel as the file type. A wizard will launch. If you take the default Project Excel Template, Project will save the file with 4 sheets. One each for Tasks, Resources and Assignments, and an Info sheet which should NOT be edited.
Users can edit the data in Excel and you can then import that data into Project by going File |Open, selecting Excel as the file type, and opting to merge data with the existing project.
You can export all sorts of data from Project to Excel but many of the other options can cuase you problems if you try to import it back to Project. Play with the different Export Maps to see what you get -- you can also create your own.
There is more that you can do but check the Project help for more ideas.
Denis