Confidence is the skill that can be learnt. However it can never be developed overnight. It needs time and patience. If we talk about giving presentation, it is high task. It needs practice. Things that can be helpful to you are:
When you are going to do a presentation, try to acquire command on the topic and understand the concept. It's of no use to talk on a topic we don't have sufficient knowledge.
The medium of communication should be one you have enough command to speak up or get a good practice of the sentences you need to repeat.
Give the presentation in a way you are teaching the audience.
Add some humor in the slides so the audience would be enjoying not boring.
It's a good practice to have a rehearsal of the presentation at home before mirror. You will learn what gesture suits you and what not.