Assuming the attendee is already registered for your event, printing their ticket is simple.
First, after logging in to LaunchTrack, find the event in question and click the "Details" button to the right of it.
Next, find the attendee in question (by scrolling or via the search bar on the upper right-hand side) and click the "View" button next to their name.
On the attendee's "Registration Details" page, click the blue "Actions" button on the top right corner, and then click "View Ticket" in the dropdown menu to open the PDF.
Once you have the PDF open, click "File" and then select select "Print" from the menu bar at the top. You can also use the keyboard shortcut Ctrl+P for Windows or Command⌘+P for Mac.