Q:

What's the purpose of F7 in vimtex? How is it used/

VIMTEX How do you enable/use the F7 key mentioned in the documentation? :map <F7> is empty and provides no clue.
EDIT: In response to the comments below. I cannot figure out what F7 is designed to do, and how to invoke it.  

A:

The <F7> key is enabled by default, unless you have other mappings either in your vimrc file or in another plugin that conflicts with the vimtex mapping.
You can use the mapping in both insert mode and in normal mode. In insert mode, you can use it to make the word in front of the cursor into a command, i.e.
test<f7>  =>  \test{

FYI: If you find the documentation for vimtex lacking or confusing, please open an issue or a pull request.

