Begin your research process by finding out what type of company you are seeking information on.
Is it -
Listed public companies (i.e. Limited companies) are entities that are listed as 'stocks' or 'securities' on an exchange (such as the Australian Securities Exchange - ASX).
It is generally easier to find information about publicly-listed companies; as they are required to disclose information about the company's operations and performance to shareholders - in the form of quarterly and annual reports.
Note that there are many public companies that are not listed in any exchange. These are known as Unlisted public companies.
Private companies (i.e. Proprietary Limited companies) are entities that are privately owned and are not traded in a stock exchange.
It can be difficult to find much information about private companies as they are not required to disclose any information to the public about their operations or performance.
A subsidiary company is an entity that is owned by a larger company (and sometimes you need to investigate a little to figure out who that ultimate parent company is).
For example, the entity behind the 'Movie World' theme park located at the Gold Coast is a private company called Warner Bros Movie World.
Warner Bros Movie World sits under a holding company called Village Roadshow Theme Parks Pty Ltd.
Village Roadshow Theme Parks Pty Ltd is one of many subsidiaries under a publicly-listed 'parent company' - Village Roadshow Limited (ASX: VRL).
The parent company is not required to produce separate reports for each of the subsidiary companies they own. Which is why sometimes it can be a little difficult to find information on subsidiary companies.
In cases like this, you can try finding financial and operational information about the subsidiary companies within the parent company's report.
Not-for-profit organisations are entities that operate to serve the community and do not generate profits. All earnings are generally re-invested back into the organisation to serve the community.
Common examples of not-for-profit organisations include medical centres, childcare centres, sports clubs, registered charity organisations etc.
The Australian Charities and Not-for-Profits Commission website provides basic financial and operational information on these entities.
Some databases, such as IBISWorld and MarketLine Advantage may also contain information on not-for-profit organisations and government entities.