To upload a file to OneDrive, go to office.com in your browser and login. Once you are on your Microsoft 365 homepage, click on the three by three grid of dots in the upper left corner of the window, like in the screenshot below.
Next, click on the OneDrive app:
Now that you are one the OneDrive home screen, click on "Add New" in the upper left corner, and then choose file or folder to upload, and browse your computer for the file.
