How to import a .csv file into onestream

I assume you are trying to import a CSV file that has data.  If so, it starts here:

If you have not already, I would suggest looking in OS Navigator to get started with the basics of data integration via a learning course.

You will need to define a data source, tie that data source to a WF import, tie the WF import to this data source and a mapping profile, and then go to that Import step in One Place for whatever scenario and year and month for which you want to import.

Your ask was pretty generic so these are just some basic steps to get started.  Again, taking a training course on Navigator may help you more.