You turn the adjusters counter-clockwise to tighten the cable tension. Do it maybe 1/4 turn at a time. If you think about the way your derailers work, the spring is always trying to move the chain. It's the cable tension that creates the balance through counterforce. So, your RD is always trying to pull the chain down to the smallest cog on the cassette. If your chain is dropping down two gears when you try to shift, for example, your cable tension isn't sufficient to overcome the force of the spring. If you shift and nothing happens, then you need more cable tension. Pretty simple, but it takes some getting used to.

You probably have a second cable tension adjuster on your RD, by the way. I always use this one when the bike is on the stand because it's a lot easier to reach than the one on the shifter.

FWIW, putting the bike on a stand and adjusting the cable tension that way is a lot easier than trying to do it while you're riding. I just make minor adjustments with the barrel adjusters when I ride, if necessary.