Probation period


I am looking to hire a UI/UX designer. But, from the past experience I have learnt that it is better to work with the person for a certain period before hiring. My question is,

  1. How long should this period be?
  2. If I don’t hire post the probation period, how do I terminate the engagement?
  3. How do I make it clear to the candidate apart from mentioning in the hiring post and conversation. Documentation is important isn’t it?