how to burn a dvd from I movie 10

Hello there, Carrie.

It sounds like you are wanting to burn a movie that you made in iMovie to a disc. iMovie has the ability to share movies in a few different ways: Email, iTunes, QuickTime, an image and sharing online with the first three options allowing you to share to iMovie Theater.
To get it on a disc, you would need to export to a QuickTime file and then use Finder or a third party app to burn it to a disc.
To save the video to QuickTime, follow the steps outlined in the online iMovie Help Guid here:

Export a QuickTime file

Create a QuickTime file

1. Select a movie, trailer, or clip in the browser.

2. Click the Share button in the toolbar, and then click File.

   

3. In the dialog that appears, do any of the following:

   • Set the title of the shared movie: Click the name at the top, and type a new name.

   • Set the description of the shared movie: Click in the Description field, and type new text.

   • Set the output format of the shared movie: Click the Format pop-up menu and choose an option.

     You can choose to export video and audio, or just audio.

   • Set tags for the shared movie: Click in the Tags field, and type tag names separated by commas.

   • Set the resolution of the shared movie: Click the Resolution pop-up menu and choose an option.

     Unavailable resolutions appear dimmed.

     Note: You can export a 4K clip or movie in its native resolution.

   • Set the output quality of the shared movie: Click the Quality pop-up menu and choose an option.

     To manually set the output quality of the shared movie, click the Quality pop-up menu, choose Custom, and drag the slider to set the target bit rate.

     As you drag the slider, the estimated file size that appears below the preview thumbnail is updated.

   • Choose a compression setting: Click the Compress pop-up menu and choose an option.

   • Add your movie to the Theater: Select the Add to Theater checkbox.

   

4. Click Next.

5. In the dialog that appears, type a name in the Save As field, or leave the default name, which is the name of the movie, trailer, or clip.

6. Navigate to the location where you want to save the file, and click Save.

   A progress indicator appears on the right side of the toolbar. Click the progress indicator to see details. The indicator disappears when the operation has finished.

   

   After the share process is complete, the movie opens in QuickTime Player. A “Share Successful” notification also appears.

For the next step you will use Finder and all you need to do is insert a blank burnable disc. If you need to make multiple copies, I would recommend making a Burn Folder. Take a look at the next article for the specific details on how to burn using Finder:
OS X El Capitan: Create and use a burn folder
You do have other options when it comes to burning a movie to a disc. The next three links are some third-party applications that are available from the Mac App Store found by using the search term "burn dvd" that you might like more for customization, if that is what you need.
Toast DVD
https://itunes.apple.com/us/app/toast-dvd/id829469267?mt=12
Smart DVD Creator - Burn Videos to DVD
https://itunes.apple.com/us/app/smart-dvd-creator-burn-videos/id548598795?mt=12​
DVD Maker Pro - Video Photo Burn Lite
https://itunes.apple.com/us/app/dvd-maker-pro-video-photo/id983085050?mt=12​
Let me know if you need any more information on the specific steps of Exporting to QuickTime and burning a disk using Finder.

Thanks for participating in Apple Support Communities.

Kind Regards.