How to use the libraries is explained in the manual at https://librecad.readthedocs.io/ or our wiki at https://dokuwiki.librecad.org/ and I suspect that there is more than one thread here in the forum, all sites have search function too.
You may also find tutorials on YouTube.
At least, when the libraries don't have what you need, you can create your own blocks and library.
investing less than half an hour into Search function can save hours or days of waiting for a solution