How can I tell if a file has synced?
A file that is synced will have one of the following icons beside it:
Why are my files not syncing?
If a file is not synced, you should be able to click on the OneDrive icon in your task bar (bottom far right, example below) to learn more about what the issue is.
What do the OneDrive icon symbols or other icons next to my file list mean?
There are several icons that show the status of your OneDrive. If you want more information on a OneDrive icon you see on your screen's Task Bar or on your File Explorer file list, check this Microsoft document which has a list of the OneDrive icons and their meanings: