One pedal is for right side and the second for left side.
They are not interchangeable!
Each pedal should have small label marking if it is for RIGHT or LEFT side.
You will see small label with “L” or “R”.

See the picture:

In case the labels are missing you can still easily find out which pedal is for what side.
There is a small “R” or “L” on the side of each pedal.
See the illustration.

The left pedal must be tightened using opposite (left) rotation.