The Raspberry Pi works similar to a desktop computer in that you can hook up a HDMI monitor , keyboard, mouse. After booting it will display either a command line or a desktop screen depending on the OS you have installed.
If the Raspberry Pi doesn’t boot then check if the RED LED is on.
constant red LED = has enough power to run
blinking red LED = marginal power to run
off red LED = power problem
Then check if the green LED is blinking.
blinked green LED = SD card is being read from (LED should blink a lot during boot up and less while running)
off green LED = SD card is not being read from
If you have a constant RED LED and a blink green LED the HDMI should be on.
Rainbow HDMI screen = OS couldn’t load, this screen is generated by the CPU and not by the SD card.
Command prompt or Desktop = OS loaded
One thing I noticed today and that is the heat sink atop the main Broadcom processor on my RPi is heating abnormally. Is my RPi getting a thermal shutdown?
The Broadcom processor gets to around 40-50C while running. This is normal. The CPU should be around 20C higher than ambient temperature.
Thermo throttling is around 60C-80C (very gradual reduction at first and then more throttling at higher temps)
Thermo shutdown is above 80C (can cause a burn within a second of touching).
Circuits can be damaged by voltage spikes. It is always suggested that computers are connected to a surge protector.