You can login to OneDrive on the M365 environment or install the OneDrive app to your mobile device or computer. Mobile device app can be found on the app store and to your computer the OneDrive installs at the same time as Office-package. As you login to the app in your computer, you can see the OneDrive files as the files on your computer.
You can use the files offline if you have downloaded the file to your computer for offline use. Notice that the changes in the file won't save to the cloud until you have an internet connection.
You can share files inside of UEF and to outsiders. Easiest way to share a file is to access it via browser, select the file or folder and choose Share. Choose who can access the file, can it be modified and add the people inside of UEF or the outside email addresses, write the possible message, and press send. Make sure you always share the files only to the people you were meant to share it!
You can restore your OneDrive up to 30 days. You can find the option on the top right settings -button -> Restore Onedrive. You can restore whole Onedrive and find lost files. Use it carefully, if you restore the situation 3 days ago, it will lose all the modification during that period.
If you want to restore a previous version of one file, you can press the three dots besides it and choose "Version history".