The best way to try ERP5 is to use ERP5 Virtual Machine which you setup yourself. The process is well described in few OSOE lectures and involves few steps which must be precisely followed.
You can follow this link to read how to setup ERP5 Virtual machine.
You can follow this link in order to properly configure your instance using ERP5 Configurator.
You can read this link how to install an ERP5 application. In this link you can find all ERP5 Applications.
See this link how to get you started coding ERP5.