How to tighten a brake?
There are two basic adjustments that apply to all types of rim brakes (v-brakes, cantilevers, calipers):

Tension:
The cable tension from the brake lever to the brakes adjusts how responsive your brakes feel.  Tighten it up and both brake pads will engage sooner and the braking action will be harder.  Loosen it up and braking will feel spongy and you may not get enough power.  Normally you want to add tension; removing tension is only done when you put on fresh pads or if you set the tension too tight.  Adding tension periodically is important since your pads wear down over time and the cable stretches a bit too.

The easiest way to adjust the tension is to use a barrel adjuster: they're usually on the brake lever or the brake or both if you're lucky.  Add tension by turning the adjuster counter-clockwise (looking at it from the side where the cable housing goes in).

But whenever you adjust tension, you need to fix...

Balance:
This controls how far each pad is from the rim.  Adding tension will pull both pads closer to the rim, but usually one will move more than the other.  So by adjusting balance you can move the closer one further away and the other pad will do the opposite.  You want to balance the pads so that they're about the same distance from the rim and engage at about the same time.  If it's skewed (like your brakes) then you won't get as much braking power.

For v-brakes and canti's there's a spring inside each brake arm.  You can adjust the spring force by turning a small set screw on the side of the brake arm.  Screwing it in (clockwise) will pull the arm away from the rim (which pulls the other one closer).  It's best to adjust the two arms together:  screw in the closer arm first by half a turn to start, and screw out the other one by the same amount.  Check the balance and then repeat as necessary.

For caliper brakes (road bikes) there's normally just one set screw to adjust.  Turn it to see which way the brakes move.