Step 1: Try SlapOS online with slapos.org
slapos.org is a commercial cloud platform made by the SlapOS team, running SlapOS. Currently in Developer Preview pre-release, it allows developers to try and manipulate SlapOS. It will soon allow you to instantiate hundreds of different sofwares.
First register to slapos.org Cloud - https://www.slapos.org - then request a KVM virtual machine. In order to connect to your instance, you will need an IPv6 connection (IPv4 support coming soon). There are many IPv4 to IPv6 gateways. For GNU/Linux users, miredo is quite reliable. Sixxs is also good for Web access to IPv6 web sites from IPv4. And Gogonet is fine in all other cases.
You can also try to connect to other services provided by slapos.org.
Step 2: Install and learn SlapOS
The tutorial "How to Become a Cloud Provider in 24 hours and Start Doing Business" will teach you how to install SlapOS, the architecture of SlapOS, how to request instances, how to add your own nodes, how to host your own cloud if you want to, and how to add new softwares to SlapOS.
Also read some design documents found in SlapOS wiki.
Step 3: Contribute
If you want to contribute to SlapOS, please read the Join the Community document.