Simple locks - 4-5 plates, normal - 6, hard - 7-8.
Mini lock diagram, as you see it in-game.
Each plate has 7 holes, numbered left to right. Click the current pin position. Goal - position 4 (marked): pin pops up there.
Move each plate one step and back. Note which plates moved with it and where. Links can be one-way: plate 1 may pull plate 3 even if plate 3 does not pull plate 1.