Create a comfortable place to sit that has no distractions. Turn your phone to airplane mode, turn off the tv, etc.
Sit in a comfortable way with your spine upright. Sitting in a chair, or propped up on the couch is fine.
Set a timer, and start with five minutes per day for one week. If five minutes is feeling almost too easy after one week, add on one minute each day until you are at 15-20 minutes.
Simply just watch your breath move in and out, don’t force your breathing, just notice your breath. When you get lost in a thought, it’s ok, just return to your breathing.