If it's a hostess bar that you're on about then its more than likely to be the same as a "snack" bar. What happens in them is :
Its like a normal bar , only you "rent" a female to come and chat to you. You also buy them drinks whilst doing so. Kinda like these men here are worried about their ability to attract women so they rent them. It's all just some sort of "semi-cheat" on your wife kinda thing. You will usual spend around 10 - 20 THOUSAND yen per visit. Usualy it's the salarymen that go there after they finish work.
The ladys , degradingly , will chat to you and pretend to appreciate your opinions , laugh at your jokes and listen to what you have to say. you know like .. holywood actors? they pretend to not know what the other actor is going to say off the script? that sorta thing.
To sum them up : If you are a miserable , married , 40+ year old salaray man then you would fit right in in a snack bar. If you are a Nice , Young , buisnessman who accieves SOMETHING whilst they are at work then STAY CLEAR!