Here are instructions on how to practice or play around with the new Salesforce1 app on you desktop.
1. Open your Chrome browser (this seems to work the best)
2. Login to salesforce.com.
3. After you are logged on, remove the /home/home.jsp from the browser address bar. This part is greyed out on the below picture.
4. Replace the removed the text by /one/one.app then your address should look like https://fluido.my.salesforce.com/one/one.app (with the exception of that fluido part of course)
5. Then hit enter and voila… you are using the mobile app look and feel.