I would like to keep 3 or 4 previous versions of a documnet I am working on. Can I do it in LibreOffice
There is no feature like that in a default installation of LibreOffice. You may have a look at extensions (e.g this one) or search for a macro based solution.
I use a simple manual naming system that allows me to keep as many versions as I want. The hint is to provide a version numbering. Then I can keep as many versions as I want. The FILE > SAVE AS displays the name of the previous version. I use a parameter FileName yyyy-mm-dd-version. For example NewReport-2020-03-23-1.odt. The current filename will be updated to the new filename, so you only need to update the date or version number the next time you SAVE AS.
You can also set the AUTORECOVERY option to provide a backup. TOOLS > OPTIONS > LOAD/SAVE > GENERAL