TCP/IP is the protocol that makes the world go 'round. The internet is powered by IP, and almost all the traffic is TCP (a small amount is UDP, mostly games and video/voice calls where every millisecond matters, and a small amount of data loss is acceptable).
You may have heard of the 7 layer OSI stack, well similarly TCP/IP has a 4 layer stack which means at higher layers you generally don't need to think too many layers lower. At the bottom are simply bits on physical wires aggregated into frames, in the physical and data layer. Above that IP deals with packets, and routing packets to the correct IP address. Above that TCP and UDP use IP packets to manage sending meaningful amounts of data, for example connecting to a specific port on a server. Finally on top of TCP you use specific protocols like HTTP, FTP, IMAP, DNS, and SSH.
IP sends packets towards IP addresses. However you don't want to use IP addresses,
such as 160.39.63.50, but instead you want to use a hostname, like
paris.clic.cs.columbia.edu. DNS, Domain Name Service, is a protocol and server
setup that translates hostnames into IP addresses. Every time your laptop joins
a network, it gets its own IP address, the IP address of 1-3 DNS servers, and
the IP address of a router that can forward packets on to the rest of the world.
Want to find out your IP address and DNS info? On OSX and Linux run ifconfig in
a terminal. You should see something like the below:
en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 58:b0:35:7d:33:7e
inet 192.168.1.183 netmask 0xffffff00 broadcast 192.168.1.255
media: autoselect
status: active
In this case 192.168.1.183 is my IP address.