[git] How to commit a change with both "message" and "description" from the command line?

git commit -a -m "Your commit message here"

will quickly commit all changes with the commit message. Git commit "title" and "description" (as you call them) are nothing more than just the first line, and the rest of the lines in the commit message, usually separated by a blank line, by convention. So using this command will just commit the "title" and no description.

If you want to commit a longer message, you can do that, but it depends on which shell you use.

In bash the quick way would be:

git commit -a -m $'Commit title\n\nRest of commit message...'