BOINC is a software platform for public-participation distributed computing projects. Users are allowed to simultaneously participate in multiple projects and to choose how to allocate their resources for each project.
First download the core client by clicking on the below link. Then create a BOINC account, setting your preferences to specify how much your computer should be working on each project. You may view your user page to see how much credit you have accumulated as your participation proceeds. In addition, you may modify your preferences through your user page at anytime to reallocate your resources among the different projects you may be involved in.