The short answer
A contract forms when one party makes a definite offer and the other accepts it. Whether a quote, email, or purchase order counts as an offer or an acceptance often decides whether a deal exists and on what terms.
Where it fits in your case
In disputes over whether a deal was ever made, or whose terms govern.
What to expect
Price quotes are usually invitations to negotiate, not offers, unless they are definite and invite acceptance.
Counteroffers. Proposing new terms generally rejects the original offer; for goods, the UCC’s battle-of-the-forms rules may still find a contract.
Shipping goods can accept a purchase order.
Firm offers and options. A merchant’s signed promise to hold an offer open can be binding without payment; other options usually require consideration.
What we need from you
The full exchange of quotes, purchase orders, acknowledgments, and emails, in order.
Common misconceptions
“No signature, no contract.” Conduct and emails can create one.
“Our terms on the back of the form control.” Competing forms are resolved by specific rules.