This is the second step in rocketry. Click the green tab. This will transport you to the launchpad with your rocket.

On the launchpad, you will need to prep your rocket for launch.
The throttle
You will need to activate your throttle. Do this by pressing Z or holding shift. Likewise, X and control decrease your throttle.
The RCS and SAS
You need to activate your control mechanisms. Do this by pressing T-R.
The altitude
You should change your altitude reader from Sea level to Ground level to avoid deploying your chutes too low. Do this by clicking the blue tab just to the left of your altitude meter.
If you want to, you can activate your lights.
Compare your screen to mine:

Note that you can have a different rocket.

Activate your rocket by pressing space. Pressing space activates all the items in the next stage.

Then, activate your boosters and decouple your support.
Once your boosters run out of fuel, decouple them.

Then, once your main engine is out of fuel, decouple it and activate your parachutes.

When you get low enough, your parachutes will deploy.

Once your main parachute(s) activate(s), cut your drogue chutes and decouple your heat shield; they aren't needed anymore.

Have fun flight!