Lucene has a custom query syntax for querying its indexes.
Lucene Query Syntax
Search for phrase "course" in the title field.
title:"foo bar"
Since Solr accepts HTTP requests, you can use your web browser to communicate with Solr. For example, search for phrase "course" in the _fullpath field.
http://localhost:8983/solr/sitecore/select?q=_fullpath%3A*course*&wt=json&indent=true
Search multiple fields - For example, search for phrase "course" in the _fullpath field and _language field = "en".
http://localhost:8983/solr/sitecore/select?q=_fullpath%3A*course*%20AND%20_language%3A%22en%22&wt=json&indent=true