Once logging into Microsoft 365 online, down the left-hand side you can see all the Microsoft Applications. You want to select the little blue cloud icon which is OneDrive. 

It is usually the 7th icon down from the top.

Once clicking on the little blue cloud, you will be faced with this page. If you haven't used OneDrive before you will not see any files on OneDrive it will be empty.

At the top you see New, Upload, Sync and Automate.

In New, you can create a folder, create Word, Excel, PowerPoint, OneNote, Forms documents online. When creating these documents through these applications they will automatically save to your OneDrive.

Link means that you can enter a link to a file or webpage and it will be saved to your OneDrive, so when you click on it, it will take you directly to that site or file.

Upload is where you can either upload a folder or files from your computer that you are on.

If you click on Files or Folder this box will pop up and you will be able to upload as many files as you like from your computer. 

Once clicking on a a folder or file click open and it will re-direct you to the OneDrive page as before then you will see your folder or file pop up in 'My Files'.

When pressing Sync this will make OneDrive sync with your device if it is not already. So you can access your OneDrive files from your computer without going onto the online version.