Application Layer

This is where network applications operate (HTTP, HTTPS, SMTP, IMAP, POP3).

Transport Layer

This sets up the communication between the two hosts; it splits the data into packets (TCP, UDP).

Internet Layer

This adds (IP) addresses to the packets and routes the packets across the network (IP).

Link Layer

This is where network hardware operates (eg network  interface card, routers). The link layer is where operating device drivers operate.

Image Source: https://commons.wikimedia.org/wiki/File:IP_stack_connections.svg