Page layouts control the layout and organization of buttons, fields, s-controls, Visualforce, custom links, and related lists on object record pages.
Page layouts helps to determine which fields are visible, read only, and required.
Page layout should not be used as only means to hide a sensitive data from users as users can still access the records/fields from other parts of platform.
Page layouts are used to customize the content of record pages for your users.
We can assign different Page layouts to different users based on Profiles.
Please check below video for more detailed explaination: