If you are advanced and need more features than standard things on website, then you will need an add-on for the website. People that is using wordpress call this add-on as a plugin. There are thousand plugins available on WordPress plugin repository that you can download from your needs. Most of them are free to download, but some of them are paid in case you need more feature or want to use it in commercial website.
There are website called codecanyon and themeforest that you can find on getting premium of themes and plugins. One of plugin and themes that I love most is Dokan. You can download from the developer or in case you have a limited budgets on your project, you can download it from down73.com, they provide hundreds of themes and plugin for you in a GPL licenses which is mean freely to distribute. You can search on google related to what is gpl license mean and what is your right and things that you can do and not do.
You can download many plugin and themes without any restriction and without any daily download limit. The great things that there are also APK source codes that you can download. APK source codes is a codes that you can changet to generate or create an Android Application. You can upload the APK to Google Play Store and get it monetize by Admob or any other related monetization that you love. The limit is your idea, because the template is already there for you to fill it with your own contents.