What is SSH? What is it used for?

SSH is a network protocol abbreviated as Secure Shell.
The use of this protocol is to connect to a  server (machine or PC or webserver) remotely.
The main advantage of using SSH is its encrypting nature.

Understanding:

SSH is an Applcation layer protocol which provides us with a secured bridge between client (our computer) and the remote server (the PC which you want to control remotely).By this you can control any server remotely.
The virtual bridge between the client and server is very secured since it encrypts the entire data which enters the bridge.
This encryption helps in avoiding many hacker attack like Man in the Middle, etc.
The most famous encrypting method used in SSH is Hashing, since Hashing makes the decryption without the Key almost impossible.
The most common port used by SSH is port 22. By default only the port 22 is used to transfer or recieve the multiplexed TCP or UPD packets of data.

Before SSH, everyone would use TELNET but TELNET does not encrypt the data,it just sends the plain test.
But nowadays all are using only SSH because it encrypts the entire data and sends.

In Windows, you can download and use PUTTY SSH client to use SSH protocol.

In Linux, SSH is an inbuilt feature so you can directly use it from Terminal.

References:- Secure Shell