If you want to cut the strip to desired length before installing, MUST cut exactly along the scissor mark. Measure from the white controller on. Cut the redundant section off. Use sharp scissors to make a clean cut to avoid damaging circuit.
You can link them again later with 4-pin led strip connector which is NOT included in package. Just search ‘4-pin led strip connector’ or similar words for connector.
Always do test before installation after cut or link operation.