Human geography is the study of human activity. For example, tourism and the benefits and negative effects that this can have on an area, development / urbanisation and how this can be managed, pollution and global warming etc. Basically, human activities that directly relate to geographical subjects and issues.
Physical geography is the study of the natural world. For example, mountains, weather / climate, volcanoes, natural disasters, animals, seas and oceans etc. Basically anything that is about nature and how the world works.