Microsoft is an American software company specializing in proprietary software. They are also involved with a lot of free software projects and services. Concretely, they own the software repository github and they are on the board of the Linux "foundation".
Microsoft owns and sells a proprietary operating system called "Windows". There are many versions of this OS which is rumored to have improved vastly since "Windows 95" was released in 1995. We can not confirm if this is true or not. It seems more likely than not that it's actually true.
Microsoft is also behind a search engine called "Bing" which is available at bing.com. It's text search results are fine. It's image search is among the best there is, it is as good as yandex and slightly better in some areas.
Microsoft has a web browser product called "Edge". It is closely tied to their search engine "Bing" and it is bundled with their series of "Windows" operating systems.
Microsoft has a history of illegalities. It has been convicted for numerous crimes throughout it's existence.