Do you mean how to import a paragraph style into one InDesign document from another InDesign document?
If so, the simplest/built-in way is from the flyout menu of either the paragraph or character styles menu. There are a couple of options there called “Load paragraph (or character) styles” and “Load all text styles” which will let you choose an ID document and select which styles you’d like to copy over.
Also, if you copy any text from one document to a different document, the para and char styles applied to that text will be copied over with it as well (although if there’s a similarly named style in the target document, it will take precedence).
Finally, you can save and load styles using the CC library feature.
So… many ways to skin a cat!