Record Type is a gateway between the user and the page layout. By default, you can assign only one page layout per profile. Thanks to the Record Types, you will be able to offer users different page layouts when creating a record. A profile can therefore have multiple record types and access different page layouts when creating a record.
Record types also let you offer picklist values for fields of the same type.
Example: A Sales profile must be able to provide relevant information to a retail sales account and a sales account to professionals. He will also have to filter the values of picklist-type fields when choosing one or the other Record type, for a more efficient input.