Your device is compatible if it supports USB host mode. It needs to run at least Android 3.1. The simplest test you could do to determine whether it has USB host is to see whether you could connect it to USB thumb drives. If thumb drives work, then your device has USB host mode and is compatible!
If you can't access Google Play, the latest version of the rtl-sdr driver for Android could be obtained from GitHub (click on the RAW button to download).
Android 3.0 devices and below are not supported any longer. You might be able to get them working using root and an old version of the RTL-SDR driver that can be obtained from GitHub. Keep in mind that this version is no longer officially supported so if it breaks you get to keep both pieces :)
SDR Touch could be installed via a file manager on your phone. You may need to download a file manager from Google Play and open the folder containing the installation package (SDRTouch.apk). Just click on it and follow the instructions.
The button panel on the left of the app is scrollable. You could swipe up or down to reveal the additional buttons.
Your phone or tablet most likely do not provide enough juice to properly power the USB dongle. You will need an externally powered USB OTG cable or an externally powered USB hub.
This is usually caused by manually starting the driver app. The driver app is not intended to be used manually (unless you know what you're doing). The order that you should work with SDR Touch is: connect the dongle via USB - Launch SDR Touch - Press the "OFF" button. The driver app will be loaded in the background automatically. You must not press "Start stream" manually!
Generally the cause is faulty USB OTG cables or not enough power being provided to the USB dongle. Make sure your device is fully compatible. If you still believe that all cables are working properly, the dongle is powered correctly and your Android device is compatible, you could use the form on the bottom of the page to contact the developer.
Yes! SDR Touch can be used as a client of rtl_tcp via the "Remote" button. Make sure the PC is streaming with speed 1.024 msps (start rtl_tcp with the command line argument -s 1024000). Using this option, you don't need to have a USB host on your phone, rather you need an internet connection. If you want to stream the other way around - from you Android to your PC, you can use the driver app and its "Start stream" button. Keep in mind that streaming requires 2 MB/s of bandwidth, so make sure your wireless connection and router allows for this!
There is no user manual for using SDR Touch. If you already have experience with SDR software, the interface should be pretty intuitive. If you are a beginner in the field this could help you - what you can see on the screen is 1 MHz of the radio spectrum. To tune to a signal, just drag the pointer along. You could change the "signal width" by changing the size of the pointer (this changes the audio filter, mainly used for AM and SSB). In order to listen to HAM and shortwave broadcasts between 200 KHz and 30 MHz, you will need a separate hardware called an upconverter.
SDR Touch does not depend on hardware directly. Rather, it depends on a driver. As long as there is a driver for any SDR hadrware frontend developed for Android, it would work properly (there is a minor current limitation that the driver needs to stream with 1 mega samples per second, but this would be lifted soon). The goal currently is to make SDR Touch a full-featured SDR software - much like a desktop solution. Therefore the development is going to be centered on improving the app itself. Eventually drivers will be developed for other devices. If you want to have a support for any other device sooner, you might want to help! The drivers are GPL-ed and open source, so anyone can develop one. If you have the coding skills to do so, you could contact the developer for assistance. Keep in mind that you would also help other apps that do SDR on Android.
SDR Touch does not have any technical limitations regarding location of usage and can operate everywhere where it is legally allowed to. The SDR Touch development team will not be held responsible for any legal issues that might be caused by usage or possession of the app. It is your responsibility to comply with your local law before using SDR Touch as clearly stated in the Terms and Conditions you receive bundled with the app.
If you try to connect from SDR Touch remotely to your PC over your home wirless router you might encounter audio soundling like if it was slowed down. This is caused by a high sampling rate on the PC side. To fix this, start rtl_tcp with the argument -s 1024000 to set a sampling rate ot 1.024 msps.
If none of the FAQ answers above provide good help, you can get in touch with the developer. Before you send your query, make sure you have the driver error log with you. In order to obtain it, run the RTL2832U driver in Advanced mode, and press Start Stream while the dongle is connected via USB. The error log will appear.