Ing to Boundy (2012), typically, a written contract will include: Date of agreement. Names of parties to the agreement. Preliminary clauses. Defined terms. Main contract clauses. Schedules/appendices and signature provisions (para. 5).
To be considered legally binding, a document must include the valid signatures of all parties entering into an agreement and outline all the duties and responsibilities each has to the other(s).
This proves that the contract is legally binding and that you and the other parties have accepted the terms and the obligations conveyed by the document. But, you do not need to always sign contracts for them to be legally enforceable. Indeed, you can accept them by conduct or even verbally.
The assignor must agree to assign their rights and duties under the contract to the assignee. The assignee must agree to accept, or "assume," those contractual rights and duties. The other party to the initial contract must consent to the transfer of rights and obligations to the assignee.