ALL AGREEMENTS ARE CONTRACTS IF THEY ARE MADE BY THE FREE CONSENT OF PARTIES COMPETENT TO CONTRACT, FOR A LAWFUL CONSIDERATION AND WITH A LAWFUL OBJECT AND ARE NOT EXPRESSLY DECLARED (IN THE CONTEXT OF THE INDIAN CONTRACT ACT) TO BE VOID
To know the major difference between the agreement and contract, I would suggest you to go through the provision of section 2(e) and 2(Hon'ble Court) of the Indian Contract act, 1872.
Section 2(e): Every promise and every set of promise, forming the consideration for each other, is an agreement.
Section 2(h): An agreement enforceable by law is a contract.
The phrase “forming consideration for each other” relates to the words “set of promise” and does not qualify “every promise”. Therefore, a promise is an agreement without consideration. The fact that the consideration is not necessary element for making an agreement is seen from the language of Section 10 and 25 of the Contract act, 1872, though it is necessary for making it enforceable.
But if this agreement is not enforceable by law then it does not become contract but it becomes void. There may be many conditions in an agreement, and complied with the conditions prescribed therein, by the parties make the agreement enforceable under the law i.e. a Contract and non-compliance would render the agreement void.
Where a document has all features of an agreement to sell, it would constitute a contract between the parties.
You can say that every agreement, which can be enforced under the law is a contract.
A contract qua contract, however, must be consensual. It must meet the statutory requirements and reasons under the provisions of the Indian Contract Act. When a contract is entered into by and between the parties, what is determinative is enforcement of the terms and conditions to be governed by the contract, subject, of course, to the application of the statute and statutory provisions. Whereas a statutory contract would be governed by a statute, other contracts would not.
I hope you can understand the difference between the agreement and contract.