As you get the basic idea what is Salesforce and how it can be used - get your own Developer Edition Salesforce org - https://developer.salesforce.com/signup. It is free. It has all the features as a real (paid) org has. The only difference - some limits are much lower (Data Storage, API calls, etc.). This one is a must to play around with the Salesforce.
Use Developer Edition (DE) org to create a project for yourself. Create a household budget application, or an applicatino for a car service company.