In Vim 8, if it is compiled with the +terminal option, you can split the current window horizontally and add a terminal with the command :terminal or :term for short-hand.
If you want to split the window vertically, the best way I know is to do a regular vertical split with :vsp or <c-w>v. Then, split one of the windows to have a terminal window (:term), then finally move to the smaller, non-terminal window and close it.
Edit: …and literally right after I wrote this I found how to easily vertically split the terminal window…
:vertical terminal
" OR
:vert term
The terminal will open in something similar to insert mode, and pressing <c-w>N will put you in the “normal” mode where you can have regular Vim motions and can run Vim commands. Note that in many shells (I know for sure in Bash and Zsh), you can run set -o vi to be able to hit <c-[> or <esc> and use Vim motions anyways. The best part about that is hitting v when in “normal” mode where the current command is opened in a new Vim instance and is run upon exiting Vim.