You will need equipment (tables, cues, chalk, talc, balls, brushes, etc. ), a good location, a liquor license, a name that will attract customers, a business license and money to run it until you make a profit.
You'll need to find a large commercial space, and there may be local licensing requirements. Pool tables can generally be leased. If you do not already have the means to open the business, you'll have to secure funding as well.
Start by finding out what regulations there may be for entertainment venues in your area. Bars and restaurants - and pool halls, which usually sell beer if not more - are regulated differently than other businesses. Know what you're getting yourself into.