6'1, 170lbs: Do I need to gain weight?

[wrenchhands]

For breathing, hold in your breath when you are taking the weight in (that means, breathe in at the top of the squat, and hold through. For deadlift, breathe in before you lift, then hold while you lift.)

[s0ku]

As others have mentioned, you should gain some weight. It'll happen naturally, though.

My best overall advice is to make sure you have the form correct, and to note your caloric needs. These two things will help you the most in the long run. In regards to caloric needs, at the very least, make sure you eat enough to maintain your current weight. You will need to adjust this later on, specifically so that you are in a caloric surplus, but this is sufficient while you begin. And make sure you have sufficient protein. Questions for everything else will come naturally when you stumble into roadblocks.

Good luck!