How do I move our files off the office server to SharePoint?

This is one of the highest value projects a small business can do, and one of the easiest to do badly.

The mistake is treating it as a copy job. Most file servers have fifteen years of accumulated structure, folders nested nine deep, three versions of the same folder, and permissions nobody has reviewed since the person who set them up left. Copying that into SharePoint gives you the same mess with a new address, plus new problems, because SharePoint has path length limits and dislikes certain characters that Windows tolerates.

What we do instead: look at what is actually being used, agree a flatter structure, clean up permissions to match how the business is organized now, then migrate. The tidy-up is the work. The copy is the easy part.

Two things worth knowing before you start. Some line of business applications cannot use SharePoint for their data files and need to stay on a server or move to hosted, so check before assuming the server goes away entirely. And files that are constantly open by multiple people, particularly large Excel or Access files, behave differently in SharePoint than on a file share and need testing rather than assuming.