Obvious question: once you get a basic feel for this what are you expected to do with
it?
This gives you everything you need to know:
http://oreilly.com/catalog/9780596008406/
In general there is a book from oreilly with a distinct animal on the cover for almost all of the basic stuff for computer and network technology. I commend that fact to your immediate attention.
SNMP provides a means of monitoring network devices through a central manager.
It is a protocol, because it defines "who" gets to talk about what, and how the talk is formatted and transferred.
Overview:
Simple Network Management Protocol - Wikipedia, the free encyclopedia
SNMP trap is asynchronous, that is, it creates a message on its own. The message is created when there is a problem with a network device.
In order to undertand it, you need to understand UDP, TCP/IP, plus what your network looks like, so-called network topology.
The basic idea is:
1. there is a database of device information - MIB
2. a small program runs on each network device - an agent
3. A manager program runs on a computer - the NMS. This coordinates information derived from each agent.
Network devices are things like routers, switches, and so on.