I created a facet as per the documentation: https://doc.sitecore.com/xp/en/developers/92/sitecore-experience-manager/facets.html
In the "Field Name" field I tried the field name as in the item's template and also as in the Solr index. Neither worked.
How do I make it show up in the Sitecore Content Search? Are there any additional settings I have to do?
Field Nameis correct - it should be similar to Solr field name (lowercase and with underscores instead of spaces) but without the field type suffix. For example, if Sitecore field is called "Title", you should specify
title_t. You can also check Search.log for any error or info messages - usually there is a log message if something is wrong with a facet.