Find out about the legal situation.
Sometimes people become so unwell they can present a risk to themselves or to other people, perhaps through neglect or through risky behaviours. The Mental Health Act provides a legal framework to make sure such people are properly assessed and treated. When it is used the person detained for assessment or treatment is often said to be 'sectioned', and various professionals are often involved, including a social worker, the person's GP, a mental health nurse, the police, or a psychiatrist.
Information should be provided to the person involved and to their family about what is happening and which part (section) of the Mental Health Act is being used and why. If you don't understand or think something is unfair or incorrect then ask questions and request written information. Close family members may be involved in the decision whether to use the Mental Health Act and there is also a right to appeal against the sections.
For reliable information, why not check out the resources at Mind found here.