I just downloaded symbols libresymbols_v0-2_de.oxt". but info on installing was lost. How do I install into LibreOffice and how do I access it. I cannot find a “gallery” button in Draw.
Just click or double click the file and follow the prompts to install
In addition to what @AdmFubar commented, you can go to Tools → Extension Manager → click on Add → browse to the downloaded oxt file. After that you’ll see a new “theme” in the Gallery: View → Gallery. Just select the correct gallery item and drag&drop any item you want.