What is Upachara? Its simple welcoming, wram treatment, and apart from all with filled mind we should treat one with utmost patience.
This panchopachara is mainly based on how we should treat others. If a person comes to our home, hoe we greet and treat them? We initially offer them some water to wash their feets, then give them water, then we make facilities for them to bath, then provide them clothes and sumptious food.
These were included in 16 upacharas.
5 upacharas are simpler form. It includes Ghandham, dhoopam, deepam, pushpam, and naivedhyam. (Simply to control their 5 indriyas- skin-gandham; dhoopam- nose; deepam- eyes; pushpam- ears (I mean by saying namas and then doing archana); naivedhya- mouth).
This is very simple and atleast we should do this before a pooja. This panchopachara pooja can be done manasik also (Symbolically) to pacify gods. Its a must to do thing after dhyana while doing sandhyavandhanam too.