When playing bridge which bids need to be pointed out/alerted?
In general you must alert when your bid does not conform to the expectations of the people at the event/table you are playing at.
Various organizations and clubs have more specific bids and conditions that you must alert on. Some have bids that never require alerts.
You need to use "alert" when you are bidding a special convention that your opponents would reasonably be expected not to know.
One example is my "one and a half" bids using a forcing one club or one diamond.
https://boardgames.stackexchange.com/questions/3600/can-there-be-a-bid-of-one-and-a-half-in-bridge