I was opening Libre Calc to set up a grid when it crashed.
No idea what caused it nor what I can do now.
First, there is not much information provided, see Ask/Getting started . So some general comments
You can start LibreOffice from the start menu or a shortcut. It will offer to try and recover documents that were open. If you had other documents in any LibreOffice program open this is a good thing to do.
If you had no other documents open and nothing really to recover then it might be better to Restart your computer before trying to open LibreOffice again. For LibreOffice to crash with virtually nothing done the problem probably lies outside LO and restarting the operating system might clear it.
NOTE:In Windows the default for power off is hibernate, i.e. keep computer in same state. You need Restart to clear memory, etc. If you are on another operating system, things might be different)