Those buttons
 

I have been asked what are the third, fourth, fifth, and sixth in the top row.

3rd = Strike through

4th = Next

5th = Shadow

6th = marquis

To use them. Type some text. Click on the first letter and drag to the last. That is one way of selecting the text.

Then click on one of the buttons. Or maybe more.

Try it in a message, or in a test post here. This is what this section of the forum is for.

Experiment. You can't really break anything.