What are government contracts?

Firm fixed price. One agreed price for a defined deliverable. You carry the risk of it costing more than you thought, and you keep the gain if it costs less. Most small contracts are this.

Cost reimbursement. Allowable costs are repaid plus a fee. Used where the work cannot be scoped precisely in advance, such as research. Requires an accounting system that can stand up to audit.

Time and materials. Paid per labour hour at fixed rates plus materials. Common in IT and professional services.

Indefinite delivery, indefinite quantity. A framework where you win the right to compete for orders later. Winning the IDIQ guarantees nothing by itself.

The requirement is written before you are involved and rarely negotiable. The evaluation criteria are published in advance. Price alone usually does not decide it. And an unsuccessful bidder can formally protest the award, which is why contracting officers document everything and why compliance with the instructions matters so much.

Any legally formed US business with an active SAM registration, in practice. There is no minimum size, no licence to sell to government and no approved supplier list to join. The barrier is finding the work and satisfying the process, not permission.