A modal is also sometimes called a 'reveal' because it can display something that is not visible until a button has been clicked on. You can put almost anything into the modal, and the size can be changed to fit the contents.
The modal displayed above has to be closed by clicking on the closing X. There is a second modal, called 'Modal with overlay', that can be closed also by clicking somewhere outside the modal itself.
Some of the file names and ID names are used by a small java script, so if you change anything, it would be best to check with that script and use the same names there.