A personal trainer is a qualified fitness instructor who provides 1-2-1 coaching sessions with clients. They agree goals with clients and provide advice, support and motivate their clients to archive their goals.
A personal trainer will identify strengths and weakness with fitness assessments.
Personal trainers provide nutrition advice and tend to provide a dietary plan alongside a training plan. Again this is dependent on your agreed goal. Weather that is to lose weight, build muscle or to obtain a general healthy wellbeing amongst other goals.