Read the units from the outside inward

A layer groups communication responsibilities. A header gives control
information; its payload is the carried data. In these examples a link
frame carries an IPv4 packet, which carries a TCP segment or a UDP
datagram, which carries application content. This is encapsulation.

Fresh guided case: a weather update carried by UDP.
Outermost -> innermost:
Ethernet frame -> IPv4 packet -> UDP datagram -> weather update
Application outward uses the reverse order. State the direction first.

Two maps. They are teaching labels, not a claim that every protocol has one perfect box.

Internet map used in this lesson
4 application   the note or page a program sends
3 transport     TCP or UDP, end to end for applications
2 internet      IPv4 addressing on these cards
1 link          the frame on the local segment

OSI names used beside that map
7 application
6 presentation
5 session
4 transport
3 network
2 data link
1 physical
Keep this seven-layer list separate from the four-layer Internet model.
RFC 1122 says the Internet application layer combines the OSI presentation and application jobs.

Worked stack, a short note carried by UDP. Name lookup is a later lesson.
application   the note
transport     UDP
internet      IPv4
link          Ethernet frame

Separate status-note pieces for the later checks, not yet assigned to layers
Status note
TCP segment
IPv4 packet
Ethernet frame
Apply the layer responsibilities to these pieces in the later checks.