The trial version allows most features to be used. You are permitted to save images 35 times before full demo mode is activated and you won't be able to save anymore.
For the best experience, your PC needs to have a 1200x800 or higher screen, and the .NET Framework 4 installed for a small number of plug-in features. If you just recently bought the PC there is a good chance that you already have it. If you're not sure, Click here to get it. .NET framework isn't an official requirement, but some plugins use it, as well as a utility that is part of the installer that sets administration privileges.
Your computer's processor (Intel, AMD) should be recent enough that it can run SSE2 extensions. Shader level 6 is required for GPU functions.