TCP/IP, also known as Internet Protocol Suite, is a collection of networking protocols that work in tandem to transfer a data packet from one computer to another using computer networks. Though it's a collection of many protocols, Transmission Control Protocol (TCP) and Internet Protocol (IP) are the two foundation protocols, hence the name TCP/IP.
The fundamental building block of TCP/IP is addressing and routing network packets from one computer system to another. This is defined by Internet Protocol. Think of an IP as well-defined routes of road networks connecting different cities. Then TCP, which is a connection-oriented protocol, works like a parcel delivery shuttle transferring the data packets from one city to another, ensuring a 100% delivery guarantee. Because TCP ensures packet delivery, many of the day-to-day protocols we use today, including HTTP, SMTP (email), and SSH, are all built on top of TCP protocol.
TCP/IP defines a model that classifies four layers of data transmission categories. These four layers include the application layer, transport layer, internet layer, and data link layer. Basically, covering the entire journey of a packet, from the time you requested this page in your browser to the delivery of the response by the web server and rendering of the contents of this page.
The application layer is the visible part of the computer network. It includes all the protocols, including interactive programs we use over the internet, such as web applications, email, etc.
The transport layer is responsible for data packaging, including the construction and deconstruction of data into data packets so they can be transported across the network. The transport layer depends on the routing and delivery feature provided by the internet layer to send and receive data.
The internet layer is responsible for sending, routing, and receiving data packets across the network.
The data link layer represents the physical properties of the network, NIC card, ethernet cables, fiber link, and all the hardware level elements that do the actual heavy lifting of transporting digital data from one point to another over the network.