Yes you can use unlimited classes in one element. Primary is a color class in bootstrap which color is blue. col2 is about the size of its largeness in the 12 col grid system

You can have multiple class in an element if you use a space between them.

For example class="one two three four five".

If you use "-" instead you create one class with a long name.

For example class="this-is-only-one-class"

Was this mentioned in previous videos? I feel like I did not learn this. I keep typing ".primary col { }" and ".secondary col" to select the separate columns then floating them separately to the left and the right.