Taking the ball behind the stumps is a skill that becomes easier as you get used to the actions of the bowlers in your team.
Keeping is about confidence and the more time you practise catching the ball, the easier it will become.
But first you need to get your basics right.
Having adopted the correct stance, the body should rise as you judge the bounce of the ball.
Move the feet and body to get into line with the ball.
If the ball is below chest height then take the ball with fingers pointing down.
If the ball is higher then twist the head and body and take the ball with hands horizontal.