There are lots of reasons why you might want to drop a marker while recording or playing back in Pro Tools. It’s easy enough, though the shortcut key (Enter on the numeric keyboard) isn’t as helpful as it might be in these days of laptops. Even desktop Macs ship with laptop keyboards by default. So the default behaviour on a Pro Tools system is hit Enter, the create memory location window opens, you make any edits to the properties of the marker, probably including naming it, and OK’ing that window creates the marker.
Using A MacBook Pro
If you are using a MacBook Pro (and lots of us are) then you can drop a marker on the fly despite not having a numeric keypad or an Enter key by holding down Fn and pressing Return (look at the image above, the enter symbol is right there, had you ever noticed it?). That changes the Return key into an Enter key, most of the time the two are interchangeable but in the case of markers in Pro Tools Return doesn’t equal Enter.
Using Auto-Name In Pro Tools
As detailed above, by default Pro Tools expects you to name Markers (or more correctly Memory Locations) as you create them. This is what I would want most of the time but if I am dropping multiple markers quickly, for example when creating manual timing references for a tricky edit, I switch on Auto-Name (Preferences - Editing) so a marker can be created with a single keystroke.