Link for information on how to read a Heat sheet 

Individual IM races are swum in order:   1. Butterfly, 2. Backstroke, 3. Breaststroke (BR) 4. Freestyle

While the Medley Relays are swum in order: 1. Back, 2. Breast, 3. fly, 4. free

The morning of a swim meet you will write your swimmers E (events), H (heats), L (lanes) and S (stroke) on one of their arms with a Sharpie marker.  (Don't worry, it will be gone after a few showers or days of swimming!). The below picture is an example of how to write on the arm.  Write it so they can read it. Make sure you look through the relays and include any that they are swimming in also.