to connect to SAP by Qlik you have to install the QlikSAP Connector on your server. Within that, you can load datas from SAP tables by QlikView and Qlik Sense also.
To connect to the Qlik Sense server it is neccessary that your mobile device is connect to the network (by wifi, e.g.)
The most mobile devices like iphone or android don't know an user, so you have to enter your windows credentials at the login.
Check this out for SAP Connector for Qlik: You have all the info required here
Qlik sense is totally responsive. Like in other tools like Tableau you donot have to create an app specifically for mobile for tablet devices. So one application can be accessed accross multiple devices.