A few days ago I saw a video, I can't remember where and what was special about it was that under the commands in the main panel there was a row with the most used commands. How can you implement this for particular purposes in such a way that when you start mathematics it always appears.
Beside Mathematica built-in
Palettes which are basically floating window, you can access with
Palettes option in Menu Bar, there are also some built-in toolbar in
Window > Toolbar which will be shown below menu bar just like the picture you mentioned.