These days if we want to find a business we either just google what we are searching for, or use the old fashioned telephone directory. In the days before telephones they still had directories - generally local, post office and trade directories.
There is a website which gives free access to digital copies of some English and Welsh historical directories, produced and owned by the University of Leicester. The directories aren't all inclusive as they weren't published every year, and neither will they cover absolutely all the country, but they are a good place to start to find information on your English/Welsh ancestor and their occupation. Of course you can find out all sorts of information apart from that, but I'll leave that up to you!