Players evaluate their hands, and decide whether they have enough strength to take a certain number of tricks. They discuss this in a language called bidding. Each player may bid or pass in their turn, starting with the dealer. If they decide to bid, they will contract to take a certain number of tricks, in either no trumps or a suit. You can't contract for fewer than seven tricks, but there's a bank of six tricks. So instead of saying "I'm going to take nine tricks, you say "3" (= 6 + 3). A contract of 3♥ means hearts are trumps and the contract is nine tricks.
Each call must be higher than the one before, either at the same level (in a higher-ranked suit), or at the next level (in a lower-ranked suit). It goes upwards, and is called the auction. The ranks of the suits are:
The lowest possible bid is 1♣ and the highest, 7 No Trumps. When the bidding is over (i.e. when a bid is followed by three passes), the hand will be played in whatever the last bid was. If declarer makes their contract, they score points - a trick score & a bonus score.
The person who makes the first actual bid is known as the opener. (The dealer is not necessarily the opener). There are 40 high card points in the deck (4 for each Ace X 4 Aces = 16; 3 for each King X 4 Kings = 12; 2 for each Queen X 4 Queens = 8; 1 for each Jack x 4 Jacks = 4 ), so an average hand is ten points. To open the bidding at the one-level you need a hand with 13+ points, (better than average because you can't start the bidding at less than seven tricks).
Partner of the opening bidder, called the responder, should keep bidding if they have 6 + points. When you open 1♥ or 1♠ you promise at least five cards in that suit. If you don't have that, but have four+ diamonds, open 1 ♦, and if not four diamonds, open 1♣. You should always open something with a hand of 13 + points, and it's usually the longest suit, not necessarily the strongest.You're looking for the best fit (the most cards of the same suit) to play in a trump suit, and if there's not a fit, choose no trumps. This bidding system is Standard 5-Card Majors.