How to practice mindful meditation
You might want to set a timer for about 10 minutes to begin with. After some experience you should not be too concerned about the length of time you spend meditating.
Focus on your breathing
Find a place where you can sit quietly and undisturbed for a few moments.
Begin by bringing your attention to the present moment by noticing your breathing. Pay attention to your breath as it enters and then leaves your body.
Before long, your mind will begin to wander, pulling you out of the present moment. That's okay. Notice your thoughts and feelings as if you are an outside observer watching what's happening in your brain.
Keep returning your focus.
Sometimes you might feel frustrated or bored. That's fine. These are just a few more feelings to notice. Your mind might start to plan an upcoming weekend, or worry about a responsibility. Notice where your thoughts are going, and accept what's happening.
Whenever you are able to, return your concentration to your breathing. Continue this process until your timer rings, or until you are ready to be done.
This video from Headspace talks you through a similar meditation exercise. You can visit the YouTube page to see a transcript.