Docker in homeassistant

Can anyone explain what is the use of docker in home assistant or what exactly is docker ?
Also Is it okay to use hassio on a linux machine and if not then what is the other alternative ?

You have posted a ton of threads asking really basic questions that are covered by the getting started and installation guides. You seem to be ignoring everything you’ve been told thus far.

You don’t use docker in home assistant. You use docker to run home assistant if you so desire.