From the tutorials index

1: Packet Sniffing(tcpdump install and first use) by IchNiSan
2: Packet sniffing. written by yours truly.

That is some reading material regarding your first question.
For the second question:
Yes it is possible to handcraft packets. Get some information on how TCP/IP works. From the formatting of your questions I doubt your reasons on why you want to do this a bit.
If you want to learn how the different protocols laying on top of TCP/IP work I suggest you go read some rfc's (request for comments).
You can find a complete list of rfc's @:
http://rfc-editor.org/
To find out about the diferent ports being used you can either search this forum or use a search engine like google.

Buenos Dias
noODle