Network protocols are formal standards and policies comprised of rules, procedures and formats that define communication between two or more devices over a network. Network protocols govern the end-to-end processes of timely, secure and managed data or network communication.
There are several Protocols but few mainly used are listed below:
HTTP/HTTPS: Hyper Text Transfer Protocol is basic protocol which is seen before every website. This is mainly used to display pages written in HTML(Hyper Text Markup Language).
Some sites show HTTPS i.e. secure sites which has SSL Certification.
FTP: File Transfer Protocol is generally used to transfer files from one computer to other devices or vice versa.
SMTP: Simple Message Transfer Protocol.
IMAP: Instant Message Access Protocol.
POP: Post Office Protocol.
TCP/IP: Transmission Control Protocol/Internet Protocol.
UDP: User Datagram Protocol.
These can be studied in OSI Model.