Many Stack Exchange answers say to "check your CiviCRM logs" which can be found in the "ConfigAndLog" directory, or to "delete your templates_c folder". What are the default locations for the ConfigAndLog and templates_c directories?
The two directories are found side-by-side. The location varies by CMS; see below. Note that you'll need access to your server's file system. If you have FTP/SFTP/SSH access, you can use that. If you have a control panel, check for a "File Manager" plugin:
- WordPress (old):
Another option for seeing the civi logs is adding the extension CiviCRM Log Viewer which gives a link via the Admin menu to view the error log