When i have to speak in front of even 20 peoples i shake that i can not say what i need to say and the bad part i;m a manager at work

Public speaking can be difficult; there are several techniques to use to help you get over the stage fright you feel, meaning the fearfulness and nervousness. Many will say to imagine them in their underwear; although this may help in some situations, other times it can cause you even greater embarassment and stress( in example, if there is an attractive person there and....well, you know!)
I suggest you take some deep breaths and prepare what you want to say beforehand, in writing, on small cards ( like cue cards). Explaining that you feel nervous talking in front of groups will help, since most of them also have the same problem and they will all be sympathetic to you. The cards will help you to remember exactly what you need to say, as well as keep on track.
Start off by just reading the cards. As your comfort level increases, look up from the cards and look slightly over their heads, or glance briefly at each of them as you read. Relaxing as you go will help - as well as remembering most of them have the same problem, whether they admit it or not. When I first started playing music on the Worship team at church, I was nervous and made mistakes - but I kept on playing. Its been over a year now - I still make mistakes from time to time, but I am getting better. I really enjoy this Ministry, and public performance ( and speaking) is getting easier everytime.
I hope this helps - GOD bless and thanks for using Fixya!!