Below is a video on how to use all of the icons on the Formulas Ribbon. If you scroll down below the video, you can get clickable quick access to each of the icon explanations in the video shown below.

0:00 Formulas Ribbon Icons

0:05 Insert Function

1:25 AutoSum Icon

2:26 Text Icon

2:43 Date & Time Icon

3:04 Lookup and Reference Icon

3:21 Math & Trigonometry Icon

3:28 More Functions Icon

3:39 Engineering Icon

4:20 Name Manager Icon

6:38 Apply Many Names

10:03 Trace Precedents and Dependents

10:43 Show Formulas Icon

10:51 Error Checking Icon

11:00 Watch Window Icon

11:40 Calculation Options