You can create an iNails account by Registering or you can sign in with one of the social media accounts ( Facebook, Google, Twitter ). You can also skip the Sign In step and use the app in a restricted mode. ( see below )
Select the Search tab and click on the magnify glass icon. From the pull down menu either select the with Palette or with Image menu items. The latter option lets you take your own picture and select colors from the image.