How do record types work in Salesforce, and how are they assigned to profiles?

Record types allow you to offer different business processes, page layouts, and picklist values on the same object for different user groups.
Key capabilities:
— Picklist values: Each record type can restrict picklist values to a subset of the master picklist. Unused values are hidden from that record type's users.
— Page layouts: A specific page layout is assigned to each record type per profile (matrix: record type × profile = layout).
— Business processes: For Leads (Lead Processes), Opportunities (Sales Processes), Cases (Support Processes), and Solutions — define which Stage/Status values are available per record type.
Profile assignment: In a profile's Record Type settings, you select which record types are available to that profile, and set the default record type. When a user creates a new record, if they have access to multiple record types, a picker is displayed.
Permission sets: Record type access can also be granted via permission sets (Object Settings > Record Types).