People upvote your videos and you get steem dollar and steem power based on their reputation and steem power. You do not get anything from them, they do not spend anything but the upvote. DTube is based on the SteemIt blockchain.
The problem comes up after 7 days. If your video did not earn 0,2$ the past 7 days, the monetization stops and you will not get any more cash for upvotes. Additionally your video will no longer be available to playback, because the IPFS hosts your video for 7 days if there is not enough income generated. DTube takes 25% of this income to pay for the hosting. It is possible to host these videos on your own with an IPFS node, which is a simple server running a program in the background.
Assuming a beginner upvotes your video, the vote will get you 0,001$. If you get an upvote from a whale with a lot of steem power and high reputation a vote can be worth several dollars.
It can be a nice platform depending on how you want to use it. Honestly the comparison to youtube is not correct at all. You can read my experience with DTube here: 