Access Concentration is a state where you are fully with the meditation object (breath) and if there are thoughts, they are wispy and in the background and do not pull you away from the breath - you know every in breath and every out breath.
Sit in a comfortable upright posture (or kneel on a bench). You can sit in a chair or on the floor. You need to find a position you can maintain for the length of the sitting without having to make any gross movements.
Place you attention on the physical sensation of the breath at the nostrils. This might be a bit inside the nose, moderately inside the nose, or at the tip. It doesn't really matter so much where as it does to find a place and stick with it.
Just simply notice the in breaths and out breaths.
You can try counting to help you not be so distracted. Count the gap between the out breath and then next in breath. Count up to 8 and start again at 1. If you get distracted, start again at 1.
After approximately 1/2 hour (don't look at a clock - just guess), stop the counting and just pay attention to the breathing.
When you notice that you have become distracted, label the distraction with a one word label such as planning, worrying, angry, wanting, past, future, etc. The first label that comes to mind is always correct - spend zero energy trying to get the "perfect" label.
After the label, RELAX and bring you attention back to the breath (and resume counting if that's what you were doing when you got distracted).
The RELAX is very important!