IDS, Firewalls, PKI

fire bad, IDS, Firewall, PKI, good

Not sure what answer you are expecting here. There are many books, websites, and articles written about these topics.

While many of us here are capable of writing long explanations about how electricity works and so forth, you will find that typing those same terms into Google may yield more information and fewer sarcastic remarks.

If you have a specific question about how a particular technology needs to be configured or how it works at the packet-level, fire away.