Yep, it's a bit more complicated than it used to be...
Go to: Tools > Customize > Interface
Under the "Customize" tab, expand the Menus list
Pick the command you want from the Command List, then Drag & Drop it into one of the menus listed under the Menus List (I hope that makes sense... )
If the command you select doesn't have an icon, you will have to create one.
In the properties area, select either "small image", or "large image". Click the "..." box and choose an icon you have previously made. Or, scroll thru the box of icons shown under "button image" and pick one from AutoCAD's database.
Right click in the toolbar area, but not on a toolbar. A menu of toolbars will appear. Pick the draw, modify, dimension, or any other toolbar you need.
You can customize these toolbars by using the method in my previous reply.
If this does not help, you will need to be more specific with what you are asking.