Instead of having a CPU, a GPU, a USB controller, and memory each on their own individual chips, Raspberry Pi uses a system-on-a-chip with all those components on a single chip.
The Pi itself can consist of a printed circuit board which boots up from an SD memory card.
Here are some accessories,
A power supply - Raspberry Pi doesn’t come with one, so we need a micro USB compatible cable in order to plug it into the wall. Use a 5V micro USB power supply to power your Raspberry Pi. Be careful that whatever power supply you use outputs at least 5V.
A case for Pi
An HDMI cable or RCA video lead - Pi can either plug it into a computer monitor with HDMI input using an HDMI cable, or can plug it into an analogue TV with a standard RCA composite video lead
A USB mouse and keyboard - wired or wireless mouse and keyboard can be interact with the Pi.
Internet connection - To update or download software, we can connect Raspberry Pi to the internet either via and ethernet cable or a wifi adapter.
An SD memory card - You’ll need one to boot up the Pi.