A packet is a formatted unit of data transmitted throughout the computer network. A packets has two things which is control information and payloads. By examining this packets we will be able to determine what is going on in our network. Hacking attempts or scanning can be recorded if we are able to successfully decipher those packets.
Wireshark is a software which analyze a networks packets and capture it in the most detailed picture available. This software is free and open source so it’s really easy to access it and used it. Also, basically it has the same functionality as TCPdump so if you aren’t able to use it you can use TCPdump instead because at the core they are one and the same.