The ability to count is the most underrated of the skills that new players should work to acquire. Learning to count can help you avoid countless mistakes. When counting becomes so automatic that you don’t even have to think about it, you are on your way as a bridge player.
You are already counting by adding up your HCP to determine whether you should open the bidding. You are counting HCP to decide if your hand is strong enough to bid at the two level over your partner’s opening one-bid. You have already started learning to count in your handling of trumps.
When you and your partner have an eight-card trump fit, you have learned to observe the opponents when you are pulling their trumps as you play the contract. You know that if you have four trumps in your hand and four trumps in dummy, and both opponents follow to the first two rounds of the suit, there is only one trump outstanding.
You also know that the trump suit in this case is divided 3-2. If one opponent shows out on the second round of trumps, you know that the suit is divided 4-1.