OSI Model:

physical layer

• how devices talk to and listen to mediums like wires
• physical structure
• Coax, Fiber, Wireless, Hubs, Repeaters

data link layer

• What devices say and listen for to talk to devices connected to them through a medium
• Frames
• Ethernet, PPP, Switch, Bridge

network layer

• What devices say and listen for to talk to devices connected to them through other devices
• Packets,
• IP, ICMP, IPSecs, IGMP

transport layer

• what devices say and listen for to maintain conversations with other devices
• End-to-end connections
• TCP, UDP

session layer / presentation layer / application layer

(these bleed into each other, think of them as one layer)
what devices are actually interested in saying to each other

session layer:

• Synch and send to port
• API's, Sockets, WinSock

presentation layer:

• Syntax layer
• SSL, SSH, IMAP, FTP, JPEG

application layer:

• End User Layer
• HTTP, FTP, IRC, SSH, DNS