Tempo refers to the speed of the movement. A tempo is specified in four numbers/Xs (e.g., 30X1) -
eccentric phase
pause
concentric phase
pause
The digits in the tempo represent time (seconds) for each phase of the movement, and 'x' means 'as quickly as possible'. Tempo free means no tempo is specified; in this case, move at a tempo that works well for you.
You must consider the concentric and eccentric phases of the movement to apply the tempo correctly as shown in the examples below.
Back squat - 5 x 3 @ 70%, tempo 30X1 = 3 seconds down to the bottom of the squat (eccentric phase), 0-second pause at the bottom position, stand up explosively (concentric phase), and a 1-second pause at the top before starting the next rep.
Deadlift - 5 x 3 @ 70%, tempo 40X1 = lift the bar explosively (concentric phase), 1-second pause at the top, 4 seconds to return the bar to the floor (eccentric phase), 0-second pause at the bottom before starting the next rep.