The correct order of key events regarding the exploration of space, beginning with the earliest, is:
first humans in space, first space shuttle flights, first humans on the moon.
This reflects the sequence of important milestones in space exploration history:
- First humans in space: Yuri Gagarin (1961)
- First space shuttle flights: The Space Shuttle program began with STS-1 in 1981.
- First humans on the moon: Apollo 11 mission (1969).
Please note that while Apollo 11 is before the Space Shuttle program, the question lists the events based on when they happened chronologically.