This is a huge subject. The liver is involved in detoxifying everything that is taken into the body. Trouble with the liver shows itself in many ways lots of which are not specific to liver trouble. There may be jaundice - yellow pigmentation of skin and mucous membranes, inappetence, weight loss, vomiting, diarrhoea, malaise and lethargy. Causes of trouble can vary from infections through toxins to cancer. It is a large and complex organ.
Investigation of liver disease may involve blood tests, ultrasound and biopsy.
There are lots of ways to help many liver conditions but not all unfortunately. Early diagnosis is the key.