A Track is part of the chaos campaign system. The idea is that you can run a unit with minimal paperwork following these rules. The players have a pool of Warchest points, which are used to repair damage, upgrade and purchase equipment, and to go on missions - the tracks that have been mentioned.
A track will have a warchest point cost to go on, one or more objectives that net the players points if they fulfill them, and optional extras which make the mission harder, but give them more points if they attain any objective.
Generally, the players will go on a number of generic tracks such as recon runs, objective raids and so on, building up points on low risk/low return missions until they choose to undertake a touchpoint mission, which will be a pivotal operation.
The following products contain full (or near full) chaos campaigns:
Starterbook: Sword and Dragon (2 interlinked campaigns, pitting a Davion and a Kurita unit against each other shortly before the Clan Invasion)
Starterbook: Wolf and Blake (2 interlinked campaigns, pitting Wolf's Dragoons against Word of Blake in the Jihad)
Era Report: 3052 (touchpoint tracks for all Clan fronts, so you probably won't be able to use them all in a single campaign)
Era Report: 3062 (touchpoint tracks for various conflicts, including Operation Guerro and Operation Bulldog, so you probably won't be able to use them all in a single campaign)
Operational Turning Points: Red Corsair (Covering the pirate raids detailed in the novel Natural Selection)
Operational Turning Points: Falcon Incursion (Covering the Jade Falcon Invasion of the Lyran Alliance circa 3058, detailed in the novel Malicious Intent)
Operational Turning Points: Death to Mercenaries! (covers the conflict between Wolf's Dragoons and the Draconis Combine in the 4th Succession War, as detailed in the Wolf's Dragoons sourcebook and the NAIS Military Atlas of the 4th succession War)
The Jihad plot books (Blake Ascending, Hot Spots 3072, 3076, Terra, Jihad: Final Reckoning) - this is a roughly contigious campaign.
Beyond all this, the Jihad, Historical and Dark Age turning points books all have individual tracks to add into your own campaigns.
Also, War of Reaving contains a system for creating your own tracks in some detail, and there's a small campaign using tracks in War of Reaving Supplemental.
You can download a free Chaos Campaign sourcebook
here.
OK, now that the crazy infodump is out of the way, and before you buy a ton of books - you need to ask what kind of game you're planning to play? Are you going to do more tabletop BattleTech fights, or have the players out of the cockpit roleplaying? If you're leaning towards RPG play, are your characters all going to be warriors, or will there be techs and other non-combatants?
If you're going to go for tabletop fights then a track system might be a good way to keep things going, and to generate games nice and easily. That said, there are no Klondike era tracks, so you'd have to generate the touchpoints yourself.
I'd recommend picking up Historical; Operation Klondike to get some inspiration for games (it has no tracks, but lots of background material to inspire your games), and then talk to your group bout what kind of game you want to play. If you're going more for RPG play, then write up adventures and a campaign like you would for any RPG.
If you're going for BattleTech play instead, maybe pick up an operationsl Turning points PDF to get a selection of basic tracks and an idea on what touchpoint tracks should look like. War of Reaving would be a good choice as well to get track rules specific to the Pentagon worlds, but not essential.
