For Salesforce users, there is an app for iOS and Android to login from mobile. Is there a respective app for communities? Or users should login via safari/google chrome into their communities from their mobile devices ?
Communities are accessible via browser, mobile or desktop.
If you want to convert the community into an app, there is a an offering by Salesforce called Mobile Publisher which creates an app via clicks. It requires a license though.
To see how your current community will look like, you can install Mobile Publisher playground(Early release) from Android or iOS store and check it.
You can also create an app of your own which wraps your community in a Webview.