Google will automatically select the sitelinks for your site based on traffic to subsections of your site. It takes a bit of time, but eventually it will show

Google will automatically select the sitelinks for your site based on traffic to subsections of your site. It takes a bit of time, but eventually it will show up. As well, if you don't like the sitelinks that Google picked for your site, you can remove them through www.google.com/webmasters