Links are the lifeblood of good SEO practices - Search Engines look at what sites are linking to you and raise your rankings if you have good sites linking to you. On many webmaster boards you can find people to trade with. You link to them and they link to you.

Or you can do a link trading called ABC - where you link to site A, site A links to site B and site B links to you.

No matter how you set up the links - many times you can arrange a trade and the person you are trading with is less than honest or just careless and they take the links down. To track each link by hand can become an impossible task so programmers came out with various options to track your trades. There are lots of Free ones - but I like Link Organizer BEST!! This is a script that you install on your server and can access from anywhere. Check it out here.