title: Some beginner's questions about MongoDB
body: <p>I'm a beginner with MongoDB and I've some questions:</p>
  
  <ol>
  <li><p>When I'm connected to Mongo, and i execute <code>show dbs</code> I see 2 databases: <code>admin</code> and <code>local</code>. What's their role? Then if I execute an insert command like <code>db.foo.insert({"value":"mongo"})</code>, the <code>test</code> database appears. Why? How can i specify a custom name for a database?</p></li>
  <li><p>With <code>show dbs</code> I get the databases (somehow like <code>show databases</code> in sql), how can I then list the collections inside a database (I would use <code>show tables</code> in sql)?</p></li>
  <li><p>When executing a command, the MongoDB tutorial always uses the <code>db</code> object. Is it the main object (a sort of "connection" object) that has to used for executing commands or it's something else?</p></li>
  </ol>
  
  <p>Thanks!</p>