If you have your own videos that you'd like to use, and you know that there will be a reliable Internet connection when it comes to presenting and/or allowing people online to view your Prezi, then you can really take advantage of the Insert YouTube option and use your own videos.
It will definitely be beneficial for you to create your own YouTube account. If you already have a Google account, then you'll be able to use those details to access YouTube. If not, then just click on the Create Account button from the home page and enter your e-mail address and details. There are lots of benefits of having your own YouTube account, but the main one for you right now is the fact that you'll be able to upload your own video files and then link them to your Prezi canvas. This saves you the time required to insert large video files directly into your Prezi and increase the file size.
There are a number of ways to create your own...