From the Summary: "The purpose of the reconciliation process is to enhance Congress's ability to bring existing spending, revenue, and debt limit laws into compliance with current fiscal priorities and goals established in the annual budget resolution. In adopting a budget resolution, Congress is agreeing upon its budgetary goals for the upcoming fiscal year. Because it is in the form of a concurrent resolution, however, it is not presented to the President or enacted into law. As a consequence, any statutory changes concerning spending or revenues that are necessary to implement these policies must be enacted in separate legislation. Budget reconciliation is an optional congressional process that operates as an adjunct to the budget resolution process and occurs only if reconciliation instructions are included in the budget resolution. Reconciliation instructions are the means by which Congress can establish the roles that specific committees will play in achieving these budgetary goals. Reconciliation consists of several different stages, which are described in this report."
CRS Report for Congress, R44058
Congressional Research Service: https://crsreports.congress.gov/