1. Ports are logical connections which help in identifying which service or program on a server would be used.
2. Ports are always associated with an IP address.
For Ex - Let's consider we open google by typing www.google.com in the URL of a browser. Below are the things happens in the background -
Name Resolution using DNS - This is to make sure FQDN's are converted into IP address which can then be processed by the computers.
Once name resolution is done, Port 80 for http or Port 443 for https will be appended with the URL IP.
Lets consider www.google.com resolve to 142.250.194.228 & https is used in the URL, hence we will get something like - 142.250.194.228 : 443
Now here, IP address (142.250.194.228) would be helping in identifying the location/ country where the server is hosted. Once the server is located, then port number (443) would be used to determine https service from the server would be used.
3. There are three types/categories of Ports-
Well Known Ports : Range [0-1023] - Mostly used by well known global services such as FTP,DNS,DHCP, HTTP, HTTPs and many more.
User or Registered Ports - [1024 - 49151] Companies/developer can use this to register their product / service.
Empheral Ports - Range [49152 - 65535 ] These are used for creating outgoing connections from the server. These are assigned by the Operating system dynamically.
Below are some common ports used day to day -
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