We use open as an adjective to mean ‘not closed’:
I stopped the car when I realised that the door was open.
Not: … that the door was opened.
Opened is the past form of the verb open:
Can you open the window, please? (present)
She opened her eyes and immediately looked at the clock. (past)
We don’t use open to refer to turning on taps and switches:
Please turn on the taps separately.
Not: Please open the taps …
Can you switch on the lights, please?
Not: Can you open the lights …