A Schedule of Values (SOV) breaks a contract's lump sum into line items — mobilization, foundations, framing, drywall, and so on — each with its own value. The line items sum to the contract total and become the framework for billing.
Every pay application bills against the SOV: each period you report the percent complete on each line, and that drives what you can invoice. A well-built SOV makes billing clean and defensible; a lumpy one invites disputes with the owner or the sub over what's actually been earned.