Anatomy of the Raspberry Pi

Raspberry Pi Model B

1. GPIO Headers
2. SD Card slot (This is on the bottom side)
3. Display DSI Connector
4. Micro USB Power
5. CPU/GPU
6. HDMI 
7. Camera CSI Connector
8. Ethernet
9. LAN controller
10. USB 2.0 port
11. Status LEDs
12. Audio
13. JTAG Headers
14. RCA (video)

Raspberry Pi 2 Model B

1. GPIO Headers
2. Status LEDs
3. Micro SD Card slot (This is on the bottom side)
4. Display DSI Connector
5. Micro USB Power
6. HDMI
7. CPU/GPU
8. Camera CSI Connector
9. Audio
10. Ethernet
11. USB 2.0 ports
12. USB 2.0 ports
13. LAN Controller

But What Do All Of These Parts Do?

Status LEDs - These diodes are indicators of what happening on our RPi. PWR lights up when we have the RPi plugged into a power source. This could help us with troubleshooting, for example, if your RPi stops working and the PWR light isn't on it could be a faulty power cord (or maybe we forgot to plug it in!). The other one you'll want to pay attention to is the ACT light

HDMI - Stands for High Definition Multimedia Interface, this is what connects us to our HD monitors/TVs.

SD Card slot - You'll notice on the two versions of the Raspberry Pi listed above, the older version uses an SD card and the newer version uses a micro SD card, so if you dont already have an RPi and are planning on getting on, make sure you get the correct SD card! The SD card is important because this is where we install our OS (Operating System) -- Without it, our RPi will not be able to boot up! On the RPi 2 you'll want to make sure the SD card clicks in, and you'll want to click it inward again to get it out without damaging the SD card.

Micro USB Power - This is a 5v Micro USB power connector, and is required to turn your RPi on. You may notice that this is the same as a phone charger that you would use for (most) Android phones! Just make sure that you aren't using anything above 5v as you might "fry your pi"!

Audio - This is a 3.55-millimeter jack to connect the RPi to an audio source, such as speakers or headphones!

GPIO Headers - This stands for General Purpose Input/Output, and they serve as connection points to connect out RPi to the outside world, but you can think of them more like switches.

USB 2.0 port - Stands for Universal Serial Bus. This where we can plug in things such as keyboards, a mouse, external storage like USB drives (aka thumb drives), WiFi dongles, etc. The older version of the RPi only has two of these, but the RPi 2 has a total of 4. However, if you run out slots you can also plug in a USB Hub, which will give you more as well!

Ethernet - If you don't have a wireless network or WiFi dongle, the ethernet port allows us to plug in directly and access the internet.

RCA (video) - This jack lets us connect to old school analog TVs. This is a separate option from using HDMI, which is a digital connection. HDMI is preferred because digital is less glitchy than analog, and HDMI does both video AND audio (less cords!). If you use this port, you'll also need to make sure you have something plugged into the Audio jack if you want sound.

CPU/GPU - Stands for Central Processing Unit (CPU) and Graphics Processing Unit (GPU). The CPU is what deal with everything that makes the computer work, and the GPU deals with graphics output