Question

which is the use of b button available in the font group​

Answer 1

Group names are at the bottom of the Ribbon and groups are separated by a thin line. Most but not all groups have a dialog launcher button in the bottom right corner of the group. The Home Tab shown above is a screenshot from Word 2010. The Home tab has varied slightly through Word versions. These variations are shown at the end of this page.

Word 2019/365 has added a sixth group at the far right: Voice. It holds a Dictate button.

I do not pretend to know what every control does, especially the ones on the dialog boxes. I will tell you what I know. If I am speculating or guessing, I will try to make that clear. As I learn more, this page will be changed. This is a "work in progress."