The document discusses various aspects of performing contracts including: 1. The requisites of a valid tender including being unconditional, for the whole quantity, by an authorized person, at the proper time and place, and to the proper person. 2. Circumstances where contracts do not need to be performed such as when performance becomes impossible or the parties agree to modify or rescind the contract. 3. Who is responsible for contract performance - the promisor, their agent, legal representatives, or a third party. Joint promisors' obligations can devolve through default or release. 4. Time and place of performance depends on what is specified in the contract or prescribed by the promisee