Typing brew install cmake as you did installs cmake. Now you can type cmake and use it.
If typing cmake doesn’t work make sure /usr/local/bin is your PATH. You can see it with echo $PATH. If you don’t see /usr/local/bin in it add the following to your ~/.bashrc:
export PATH="/usr/local/bin:$PATH"
Then reload your shell session and try again.
(all the above assumes Homebrew is installed in its default location, /usr/local. If not you’ll have to replace /usr/local with $(brew --prefix) in the export line)