DMCA gets hosts out of being fined for user uploads or even having to think much about it. YouTube has their own system that goes well beyond DMCA, probably because they want to encourage the copyright owner to agree to accept monetization of the infringing material instead of having it removed.
For a host that just sticks to DMCA it is quite simple.
1. A claimant alleges that a user is infringing their copyright.
2. The notifies the alleged infringer and removes the content.
3. If the alleged infringer disagrees that the content is infringing they notify the host.
4. The host notifies claimant that the user disputes the claim, and gives the claimant the user's contact information.
5. If the host does not receive within a couple weeks proof from the claimant that the claimant has filed a copyright infringement lawsuit against the user the host puts the content back up.
For a host that just sticks to DMCA it is quite simple.
1. A claimant alleges that a user is infringing their copyright.
2. The notifies the alleged infringer and removes the content.
3. If the alleged infringer disagrees that the content is infringing they notify the host.
4. The host notifies claimant that the user disputes the claim, and gives the claimant the user's contact information.
5. If the host does not receive within a couple weeks proof from the claimant that the claimant has filed a copyright infringement lawsuit against the user the host puts the content back up.