Being active has it's purpose and is very beneficial in it's own way. It is important to keep active in order to relieve stress and remain healthy. An important component of health however, also makes the space to develop stillness as a means of mental and spiritual well-being. Meditation is a great way to begin to train the mind and body to the observance of the thoughts and how busy the mind actually is.
Meditation can help curb anxiety and fight off depression, meditation can also relax the mind and prevent the arising of anger. Essentially sitting is merely an on the surface practice of no movement; in reality even when sitting there is continuous movement in the mind and the arising of reactions within the body still occurs. If you are new to this practice your first attempts will help you to realize that perhaps the endless thoughts which are entertained have brought about stress and anxiety in your life. Eventually with enough practice the mind will begin to still and a regular practice will need to be maintained.
You can't change anyone but you can change yourself
Perhaps you deal on a regular basis with others that are very negative or condemning towards you, maybe you talk this way about yourself. It may just be a matter of speaking up and expressing a distaste towards the condemning behavior. However this does not always work and you really can't change a person unless they decide for themselves. Having a regular practice will help you to observe the actions of others so that they do not personally affect you.
When you begin your practice you want to find a comfortable seated posture but you don't want to be lying, leaning or too relaxed. This is because you can get tired when meditating and end up falling asleep! There should be an awareness of the body and the breath and this is the start of your practice. You will find that the thoughts which arise can hold you captive and you will need to continue to bring your awareness back to the breath. After awhile you may feel discomfort in the body and from there you will begin to observe the discomfort. You may also feel relaxed sensations and this will also need to be observed. All which arises in your practice should be viewed as a passing phenomena. For your first sit try 5-10 minutes and slowly increase to 20-30 minutes.
The following video will help you get started with a meditation practice: