I cannot sit more than 20 mins and even I try to see my breath but still cannot go deeper.
The very happy news is that the science of yoga offers many tools to assist you in going deeper in meditation. You can start by discovering the most comfortable meditation seat for you, as it is difficult to calm the mind for meditation when the body is uncomfortable.
During meditation the use of a meditation technique is much more effective than just attempting to sit in the silence without technique. There are several ancient and very helpful techniques which are taught in various traditions. Yogananda recommended Hong-Sau, which we teach here at Ananda.
Another point to remember is that depth of meditation is more important that the length of time you sit. Especially if you are a beginning meditator, do not attempt to sit so long that the primary quality you are experiencing is restlessness. Instead seek a deep and still meditation of shorter duration, and build up length of meditation gradually.
Rather than go into a lengthy and necessarily incomplete explanation of all of the details of meditation practice here, I encourage you to take a look at our 10-week online meditation course at this link:
You would go through this course with many others from around the world who wish to learn to meditate. This course has classes with detailed teaching of the principles, guided meditation sessions, and also personal support for your questions. The 10-week course allows you to establish a strong practice, and I think you will find a powerful support for your practice by sharing the course with other students. If this is not possible for you to do, please look at our free mini-course in meditation on our website here.
I encourage you to pursue your meditation practice in whatever way is a best fit for you right now. It is one of the very best steps you can take in your life.