Rules & Etiquette
When you make an insufficient bid - that is, one below the minimum level for the suit you have bid - the usual course is to correct it to the appropriate level.
For example, after the auction 1♠ -- 2♥ --, if opener bids 2♣, this is below the minimum level allowed. He would normally correct this to 3♣, as being the lowest bid he can make in that suit.
He may, instead, choose to make any other bid, including Pass. If he does so, his partner must not bid for the remainder of the auction. He may make further bids himself if the opponents bid or double.
If, following an insufficient bid, the next player bids, passes or doubles before it has been noticed and corrected, the bid is deemed to have been accepted, and bididng carries on as normal. If this does happen, bidding continues from the accepted bid - so a possible bidding sequence might be: 1♠ -- 1♣ -- 1♥ -- 1♠ if the second opponent does pass before noticing the illegal bid.
You must never deliberately make an insufficient bid.