The short answer is, you ask the copyright holder.
The long answer is, it depends on the type of work, and your proposed use. For some uses, you can get a blanket license from a royalty collecting society that will cover thousands of works for a given period of time. For others, you will need to negotiate directly with the rightsholder for a license, which will be very specific to your use.
If you are the author, you automatically have copyright protection as soon as it is written. If you are not the author and wish to use the materials, you would not be buying the copyright; you would be seeking a license to use the materials in a specific way, and the author would still be the copyright holder.
Contact the copyright holder and see if he is willing to sell. If not, you are out of luck.
The copyright holder, or anyone the copyright holder authorizes.
The copyright holder or their appointed representative can take action.
With permission from the copyright holder, yes.
In writing.
Only use materials in the public domain, for which you are the copyright holder, or for which you have permission from the copyright holder or an exemption in the law.
The only way to be certain is to contact the copyright holder yourself.
Nothing will happen to a person who breaches copyright law unless the holder of the copyright chooses to sue the violator. The lawsuit court settlement will determine the monetary damagesowed to the copyright holder (if any).
Unless other arrangements are made, the creator of the work is the automatic copyright holder.
You need permission from the copyright holder or an exemption in the law.
Unless other arrangements were made, the creator is the initial copyright holder.
Unless other arrangements were made, the creator is automatically the copyright holder.
If you are the copyright holder, simply fill out the complaint form (link below) and YouTube will work with you to address the issue. If you aren't, you may wish to alert the copyright holder.