I would recommend reading the first couple pages, just to get an idea of what happened during the initial imperial attack on our section of Gallia. If you want to go even further, you can read the section about us training in Fort Breda to get an idea of how the squad generally behaves. Page 6 has a post about our current objectives (which are almost completes).

Currently our squad was an advanced unit sent to clear the way for a main army column approaching the city of vasel for an attack. Once it arrives (within the next couple posts), our squad (and the NPC squad that joined us) will be restructured and then held in reserve for if the attack needs reinforcements somewhere (they inevitably will).

Basic knowledge of the valkyria chronicles game is also a big plus. I'd suggest you read at least the wikipedia plot summary about it and the world it is set in. 

.... Ok, that's a lot of reading. In practice, you probably don't need to read it all, with just page 6, and the wiki summary being the most important. Everything else is just extended background which is not of vital importance.