Copyright is a legal concept, it helps the creator of an original work piece have exclusive rights to it.
Our 'OTS' will have to include sound that we've made using a programme for example 'Sibelius' or we could use 'foleying' to enhance the quality of the sound. Copyright can be seen as both good and bad, the negative side is it will take more time and effort to create these sounds rather than finding a clip out of a wide variety online.
I should only use a work that's been protected by copyright with the copyright owner's permission.
However, Copyright does not protect ideas for a work. It is only when the work itself is fixed, for example in writing, that copyright automatically protects it. This means that you do not have to apply for copyright.
More about copyright: http://www.ipo.gov.uk/types/copy.htm