This being the first level and all, everything's pretty straightforward. Look out for Akrid-generating hives, glowing areas on larger bugs and T-ENG towers that can be shot open for extra energy. There's a Vital Suit right away here, hop in, move ahead and right after the two frozen cars you'll see two energy drums. Behind them is the game's first letter token. Shoot it, get past the hives and use the VS to topple the larger Akrid. Head inside the parking garage for the first data post, ammo up and keep moving. When you come across an area infested with hives like this garage, stick to grenades and the shotgun clear 'em out fast.
Once outside, head east, past the fence towards the silos. Look behind them for your next token, the letter "A." You'll find a rocket launcher buried in the snow nearby, but honestly, the machine gun/shotgun combo will suffice. There's another large Akrid inside the next building, so if you're unsure of your dodging and blasting abilities, pick up the launcher as a backup plan. But, before you charge in, take care of the smaller hive from a distance. If you rush in, you'll have to deal with the big bug plus a horde of smaller nuisances. After the biggy's dead (ignore the glowing arms, just shoot to kill), climb the stairs in the southwest corner to find another token.
Activate the next data post, kill the arriving bugs and head up the mountain. Nothing new here, really. If you like, you can blast the discolored boulders and have them crash down on some bugs, but this special attack is put to better use in level four. For now, head onward into the bug lair.
Just inside the lair you'll see a lone Gatling gun. Use it to clear nearby hives, then head down into the pit, hugging the north wall for the next letter token. Before venturing further, be sure to ditch the larger Gatling gun and retrieve your previous weapon. Keep moving along the narrow walkway until you see a patch of glowing eggs. Shoot them, then drop down directly below to find the last letter in a small crevice. Congrats, you've just spelled EARTH and are ready to take down the game's first boss.
This guy's essentially a larger version of the only-weak-in-the-tail bugs you've seen already. With a VS nearby and some fancy shooting, you can down this bug in no time. He's a bit fast, and will curl up into a ball after he's hit enough, rolling around, flinging rocks everywhere and so forth. If you find it in this pit, the VS rocket launcher can knock him out of his spin, giving you an extra chance to rip his tail apart. Basically, just keep strafing, hovering and moving around to take this insect down.