you can gain confidence by telling yourself that you can do it always give yourself back that since others are doing this you too can do it and you will be successful.

Stop looking down on yourself or condemning yourself that you cannot do it.

Always practice when you are in your privates closet and gradually you will be bored or gain your confidence.

Never allow anybody to discourage you that you cannot do it or you cannot achieve all those things, always focus ,never get distracted.

And finally you can engage yourself in some books how to gain confidence and you will be reading them and you will know how to gain confidence.