Violating the terms of a contract is known as a breach of contract. If you breach the contract you entered into, the other party to the contract can sue you for not honoring the contract. In particular, the other party to the contract can sue you for either “damages” or “specific performance” of the contract. In a suit for damages, the other party is seeking to recover any financial loss they might have suffered as a result of you failing to uphold your end of the contract.
For example, if you hired someone to paint your house and promised payment of $1,000 once the painting was complete, if you failed to pay the painter $1,000 when the painting was complete, the painter could file a suit against you seeking the $1,000 that they would have gained had the contract been honored.
In a suit for specific performance, the other party is asking the court to enforce the terms of the contract and force you to perform your end of the deal. In most circumstances, courts will deny a request for specific performance, since courts do not like to tell people that they must or must not do something. However, if the contract involves the sale of something rare and does not involve any type of service, the court might be more likely to order specific performance. Even under these circumstances, however, courts are still reluctant to order specific performance when a contract has been breached.