Sit, get comfy, and calm down. Relax your eyes, your jaw, your shoulders, and anywhere you're carrying tension.
WHen you're settled, focus on your breathing, pick one spot (belly, nostrils, nose, etc) and count each breath in your mind. Try to count softly; you want to pay attention to your breathing, not your counting. Start at 1 and go to 10. When/if you reach 10, start over again from 1.
When you find yourself distracted by a thought (and you will), that's normal. Just acknowledge the thought, and start counting again from 1.
Get curious about your breath. Is it hard or soft, fast or slow, dry or wet, smooth or ragged? Notice the pauses at the ends of the inhale and exhale: what's it like? What are the parts in-between like as it comes and goes?
If you find the counting helpful, stick with it. If you find the counting too distracting, just try to pay attention to the breath without it.
Lastly, don't worry too much if your mind is bouncing around like a monkey on a sugar rush; that's pretty normal. Most of the practice of meditation is continually coming back to the present moment, not attaining blissful thought-free emptiness (which is quite rare, even on retreat).
Good luck
As a pragmatic matter, if the counting is distracting, try paying attention to the breath without it.
Likewise, if the breath itself is problematic (something I'vep ersonally wrestled with), try another anchor: full-body awareness, or just listening.
My favorite book for beginners is Philip Kapleau's Three Pillars of Zen. The author was a Zen teacher for many years and helped steer me in the right direction.
After one or two counts to ten (but starting over whenever I'm distracted) (which happens a lot), I usually stop the counting and just focus on my breathing, which I find more relaxing.
