Evidence that you have done this kind of work before and done it well: references, past contracts, and for larger awards, ratings recorded in CPARS. Evaluators use it to judge risk, not just capability, and a strong technical proposal can still lose to a competitor with a cleaner track record. New businesses without federal past performance can usually offer commercial contracts or subcontract work instead; check the solicitation's instructions for what counts.

In a sentence

"Offerors shall submit no more than three past performance references of similar size and scope." Pick the three jobs that most resemble this one, not your three biggest, because the evaluator is checking for a match, not a resume.