If the video has been authored to DVD (one suitable to play in a DVD player attached to a TV - not just one burnt as a data file) the file on the DVD containing the video will be a vob file which is not suitable to upload to video sharing sites like Youtube etc.
If you don't have the original file/project that was used to create the DVD you would need to convert the VOB file back to a suitable file format - mpeg, avi so that it could be uploaded. You can do this by using a freeware converter (quite a few out there - try
this one - I haven't used it but looks OK). Once converted to avi or mpeg you can upload it to video sharing site - check the site's recommended specs for videos - ususally noted somewhere in the help menu for the site.
If you do have access to the original file/project - rather than burn to DVD as your output selection, choose to make a file suitable for use on a computer - will be either .mov, .mpeg, .avi, DivX, Xvid or some similar setting depending on software used.