Most of the work you can do in ComboCurve will be organized within projects, including scenarios, forecasts, type curves, etc. Wells can be imported to the scope of a specific project too, and thus only available to be used inside that project. However, wells are special in the sense that they can also be imported to the company scope, which makes them available to be added to and used in any project.
When a company-scoped well is added to a project, it is not copied but referenced, which means that if that well (or its production data) is modified, then that change will be reflected in all projects where that well has been added. Wells imported from a spreadsheet, using the Data Import feature in the ComboCurve website, can be imported to either company or project scope, which can be selected in the last step of that process. The REST API, on the other hand, is currently limited to importing company-scoped wells.
Learn more about ComboCurve scopes: