Starting with Google or similar internet searches is not a bad way to identify companies of interest to research!

Identifying companies by type of product, service or industry area: NAICS codes
NAICS stands for North American Industry Classification System and consists of code numbers that are assigned to various industries, products and services and other business or non-profit activities.
You can search within many library databases, such as Business Source Ultimate, Mergent Intellect and others, by limiting to specific NAICS codes in order to find companies classified under those codes, as well as articles and reports about the overall industries and competitors within them.
For example 721110=Hotels, Lodges and Resorts industry.
Look up codes:
Census.gov NAICS
Below are some additional resources to help you first identify, then find background on companies / businesses.
Below, Mergent Intellect and Orbis will both find company reports and financials on public as well as many private companies. PrivCo is a directory of private companies only, with more limited information per company.
Business Search Ultimate and Factiva include mostly business journals, trade journals and business news sources.
Regional Business News includes publications with regional information.
Access World News provides general news across the US and World, including national and some regional news.
Public companies tend to be large and are traded on stock exchanges. They often are made up of corporate hierarchies with parent vs. child or subsidiary entities. It's easier to readily find financials, news, market and other details on public companies.
Private companies are often smaller, but some can be large. They are privately-owned so face fewer requirements, such as through the SEC, to be transparent about all their operations and financial details. Some library databases include some details for private companies. In addition, searching both business article databases and national and regional news article databases can retrieve information about these entities.