Why can't I edit my document in SharePoint using Excel or Word online?

  • Your browser may not be compatible. (How do I do that?) 
  • Your document may not be in the latest file format  - Office Online requires your files to be .docx, .xlsx, .pptx (How do I fix this?)
  • Your document library maybe set up to force documents to be checked out before editing. This is no longer necessary in SharePoint 2013 so can be turned off (How do I do that?)