Restart Enduro:
a series of 6-7 "test" sections (timed), often connected by "transfer" sections (not timed)
race the test sections, cruise the transfer sections
usually, trail is not repeated
racers take off every 60 seconds with a group of 4 (your row)
racers must arrive at each test section in time to take off with his/her row
lowest time at the end of the day wins

Sprint Enduro:
a collection of 2-3 "loops"
race each loop 2-3 times
trail is repeated
racers take off every 10-15 seconds individually (no rows)
racers must complete all loops within an allotted amount of time (usually 2.5 hours)
lowest time at the end of the day wins

At a 2 day event, each day is treated as an individual race. Saturday is typically less mileage so people don't get too tired to finish Sunday.