Here's a British perspective:
A pub - short for 'public house'- is a business establishment in a building that has often been in same location for many, many years. This is particularly the case with pubs in the countryside. In the majority of villages in Britain, the pub is often the second oldest building in the village : the church is the oldest (anything up to thousand years or more years old), while the 'public house' will usually be a building which is several hundred years old.
So, what can you find in a pub? Well, there's always a bar** (see below for definition), or sometimes more than one, and maybe a separate room for eating meals. Upstairs, there might be a function room which you can hire for private parties. There may also be a games room, and there's nearly always an outside area. Many pubs have gardens where you can drink and eat in good weather, and pubs which want to attract families might also have a children's play area outside. The publican or 'landlord' (who might be the owner, tenant or licence-holder) and family usually live on the premises, so there'll be living accommodation there, too. Some pubs, especially in the countryside, might also have overnight accommodation for guests, dating back to the old tradition of coaching inns.
So what's a bar, then? It can be one of two things:
1. *A bar is a long counter on which drinks are served. The staff usually serve from behind the bar, while the customers sit or stand on the other side of the bar.
2. * *A bar is also a room containing one of these long counters, plus chairs and tables where customers sit to drink and socialise. You can find bars in many places: pubs always have a bar, and hotels nearly all have bars. You'll also find bars on university campuses, in clubs (such as golf clubs and sailing clubs) and on board cruise ships, for example.
I hope that helps to answer your question.