how to add groups of apps on to dock ?
While holding down the Command key, select the apps in the Finder that you want in the Dock.
Then, just drag all of them from the Finder into the Dock.
~ or ~
If you want to have a group of apps in one specific spot on the Dock, you have to do a few things.
1. Create a new folder someplace in the Finder (command-N). Name it something useful.
2. Select all of the apps in a Finder window that you want in that one specific spot in your Dock.
3. While holding down the Option AND Command keys, drag those apps into this new folder.
-- The apps will not actually be placed in the folder, but an "Alias" of each one will be.
-- Aliases are tiny files that "point" to the real files.
-- Aliases have a tiny black arrow in the lower left corner of their icon.
4. Drag this folder into the right end of the Dock.
-- An alias of it will be placed in the Dock; the Dock only has aliases in it, by the way.
-- Now, whenever you select that folder in the Dock, your group of apps will appear for you to choose between.