How do I use a French Press to make coffee?

Buy whole bean coffee (preferably freshly roasted, maybe even from a local roaster).

Start with a rough grind. Use a burr grinder to achieve a more consistent grind. If the grinder has a french press or coarse setting use that, else experiment with it to find a consistency that produces coffee you like.

Take out your plunger and place 1 T of grounds per 4 oz (115 g) of coffee that you are making. Again you can experiment with the amount of coffee you put in to get something that suits you taste.

Use 4 oz of water per T of grounds that you put in the press. Fill your press with water no more than about 1" (25 mm) below the spout (if you have a smaller press you go a bit higher, but not too much or you'll spill). The water temp recommended is ~200°F (95°C) (just short of boiling. Stir gently, if you have a large pot use a chopstick. If you have a small pot a plastic spoon or coffee stirrer will work.

Put the plunger in the coffee and press down slightly so all of the grounds are below the water level, this will press out some of the air in the grounds and also ensure even wetting.

Wait ~4 minutes (again, experiment here to determine best flavour).

Press your pot slowly and gently. If you encounter too much resistance wait a moment (or even pull back on the press a bit) and then continue (too much resistance can indicate too fine a grind, try a larger grind next time).

When your plunger is all the way down wait a few moments and then pour. Waiting a bit allows some of the sediment to settle out of the coffee so you get less in your coffee cup. Some sediment is normal and provides body, but too much can be a turnoff. If you will not be drinking all of the coffee you made, decant it into a different pot so that it does not continue to steep in the grounds.

While there is some exact science here. A lot of what you do is informed by your own tastes and preferences. Experiment with it and see what you like. Spend some time deciding what kind of coffee, how long it steeps, how fine a grind you need and even how much sediment you like.