Useful tool for beginners
I don't know whether there is an Android version, but for an iPad, I have found this app invaluable as I have no formal training in electronics and do have some problems with the theory behind OpAmps.
It is called "EE Toolkit" and is available with limitations for free, but I found it so good I decided to buy the PRO version for about US$10.
Try it out and let me know what you think!
Looked it up on Google. says it is only available for iOS.