[nicky0]

Generally you have to find the code to the lock, to open the cabinet, to get the key, to open another door ....

A sequence of puzzles which unlock the next step.

Puzzles like the code lock may be numeric, you may find a clue to the code as a sequence of colors, which you have to find the color key for (maybe it is split into parts and hidden around the room).

Sometimes it's as simple as finding a key. e.g. in the pocket of a coat hanging on the wall, or a note inserted into a book on a shelf. (Tearing the room apart to find objects is usually the best strategy!)

Some puzzles get a bit more clever than this but these are usually the foundation elements.