At the time of writing, OC6 is the latest and its installation for 3rd party Apps involves:

  1. download from Apps page
  2. uncompress downloaded files to sub-directory /apps
  3. login as Admin to Enable installed Apps

Occasionally, an App might be incompatible causing OC to fail to load.  With sqlite installation, here is the fix.

Example: MoveFiles app

[server]$ sqlite3 owncloud.db
SQLite version 3.5.9
Enter ".help" for instructions
sqlite> update oc_appconfig set configvalue='no' where appid='movefiles' and configkey='enabled';
sqlite> .quit
Installing ownCloud apps