The Edit Offline action lets you download a file to your computer so you can edit it there. This locks the file in the library to prevent others from editing it simultaneously. It's available for every file.
The Edit in Microsoft Office action lets you edit a file in the appropriate MS Office program. The file is locked in Alfresco while it's being edited. It's available only for Microsoft Office 2003 or later files.
The Edit in Alfresco action lets you edit plain text, HTML, or XML files directly in the document library. It's available for these file types, which can all be created with the Create feature in the library.
The Edit in Google Docs action lets you work with files in Google Docs. The file is locked in Alfresco while it's being edited. It's available for supported document, presentation, and spreadsheet formats.
You can also edit the properties of a file, or upload content as a new version of an existing file.