How to add an About dialog before the settings in the ActionBar?

Do you know how to create a menu about in the ActionBar and show a dialog?

first of all i recommend you to use google for your question.because you can find dozens of websites and questions about this issue.But since you are a starter i will try to give you an answer.

That three button thing on your action bar is for menu items.which you can add it with the following tutorials by google itself.

MENUS

HANDLING CLICK EVENTS

On its on click event you may want to use dialog window(which you can also google it and find) but here is the link for it.

Dialog

Here is one custom dialog example.

Custom Dialog

with this links you may want to have this menu and dialogs if you just follow the instructions.