Hi Annemarie,
You can install OJS on your local machine, whether it is Windows, Linux or OS X, so long as you satisfy the system requirements (
http://pkp.sfu.ca/ojs_download). Specifically, if you are running OS X or Linux you should have a recent version of Apache installed, and should check that you have appropriate versions of PHP and MySQL or PostgreSQL installed and configured. If you are running Windows, you should have Windows Server or Apache running, along with PHP and MySQL/Postgre. If you can give us more details on your operating system, and maybe an idea on your technical skill level, we can point you in the right direction.
Cheers,
James