"He wants to sell the white toga."
Translation:Togam candidam vendere vult.
It is similar to when you would use 'me' instead of 'I', 'them' instead of 'they', etc.
togam candidam is in the accusative case since it is the thing the is wanted to be sold.
toga candida could be the nominative and would then be the subject of the sentence making it 'the white toga wants to sell'.