Catalyst Game Labs has released a Battletech Primer for those new to the game and the following link to a New to the Boardgame page. 

"Initially published over thirty years ago as a tabletop board game, BattleTech has gone on to become one of the gaming industry’s most important and longest-lasting science-fiction universes. In the free pdf BattleTech Primer (62.05 MB)  PDF above (it’s 65 megs, so may load slow depending upon your internet connection) we will explore a little of the property’s history of products and skim the surface of BattleTech’s incredibly rich fictional setting."