• task[s]
• project[s]
• folder[s]
• tag[s]

• name (string)
• note (string)
• primary tag (tag) (creation only)
• tags (list of tags) (modification only)
• flagged (boolean)
• completed (boolean)
• creation date (date)
• start date (date)
• defer date (date)
• due date (date)

• name (string)
• note (string)
• singleton action holder (boolean)
• sequential (boolean)
• creation date (date)
• start date (date)
• defer date (date)
• due date (date)

• name (string)

• name (string)

Below, "task" means the literal string "task". "tasktype" means a reference to an object of class "task".

• make new (task|tag|project|folder) with properties {property:value[, property:value...]}
• move (tasktype|tagtype|projecttype|foldertype) to (end of (tags|projects|folders) of (tagtype|projecttype|foldertype))
• remove tagtype from tags of tasktype
• add tagtype to tags of tasktype
• set (tasktype|projecttype) to the parent task of tasktype

• (task|tag|project|folder) whose name is string
• (task|tag|project|folder) where its name is string
• flattened (tasks|tags|projects|folders): retrieve matching items without having to locate them within a specific hierarchy

tell front document of application "OmniFocus"

  -- Create a new project and save to variable `theProject`
  set theProject to make new project with properties {name:"Project Name", singleton action holder: true}

  -- Create a new task and save to variable `theTask`
  set theTask to make new inbox task with properties {name:"Task Name", note:"Task Note"}

  -- Move `theTask` inside of `theProject`
  move theTask to end of tasks of theProject

  -- Create a new task directly inside `theProject`
  tell theProject
    set theOtherTask to make new task with properties {name:"Other Task Name", note:"Other Task Note"}
  end tell

  -- Create a new tag
  set newTag to make new tag with properties {name:"New Tag"}

  -- Add `newTag` to `theOthertask`
  add newTag to tags of theOtherTask

  -- Create a new task with `newTag` in Inbox
  set theThirdTask to make new inbox task with properties {name:"A Third Task", primary tag:newTag}

end tell

The following scripts and guides were an enormous help and this guide wouldn't be possible without them:

• https://gist.github.com/matellis/69954d4212b1a36c13aad3de4e75187e#file-things3-to-of3-applescript-L350
• https://gist.github.com/AnilRh/8a0b372ffa9c4a68d6eb
• https://colterreed.com/create-omnifocus-project-templates-with-applescript/
• https://github.com/anastasiuspernat/The-Hit-List-2-Omnifocus/blob/30e4671eb2d926ff3789e9c8bacb95c60a478e4d/%5BTHL%5D%20to%20%5BOmnifocus%5D.applescript
• https://github.com/jacobsilver2/OmniFocusDailyProjectTemplate/blob/4de69359de5aa249988361473439581c8b57d77e/dailyOmniRoutine.applescript
• https://github.com/ryuiwasaki/Omnifocus2-AppleScript/blob/2ccd777c33ad15867f6fdf5f72db8459802a44d5/Omnifocus2SyncEvernote.applescript
• https://github.com/Rahlir/OmniFocusScripts/blob/3f3ef4b0502d7e32aece5ead423d0f195778619d/Scripts/omnifocuslib.applescript
• https://gist.github.com/aderyabin/1465125
• https://gist.github.com/cdzombak/11265615