I havent bought one yet, but i want to know how is it being folded-unfolded?

For example, if its currently folded (closed), and i want to open it, i probably lift the propeller wings up, and what happens next? Is there some lock mechanism which clicks and keeps propeller unfolded (open) from now ?

Centrifugal force when the motor spins keeps it open. Drag when the motor stops closes it back up. Some use a weak rubberor elastic closing strap or spring

thats actually great. thankls

Your ESC must have a "brake" or the prop will not fold back when the engine is shut off. Without the "brake" the prop will just windmill (and create drag).