I'm a bit confused by your question. Are you hosting WordPress locally for development, or are you referring to uploading files to WordPress on your webserver through WP-Admin?
Uploading media files (pictures, videos, etc) to WordPress through the WP-Admin in a web browser requires the Flash Player browser plugin, which I've heard Apple isn't shipping with new Macs. Go to the Adobe website and download the latest version of Flash Player. Or, you can use the "browser uploader" version alternate option.
If you are running WordPress locally, you'll have to set the file permissions on your computer along with the localhost apache settings.
Hope that helps.