In your build.gradle
file of main module(app), define your minimum and target version number.
android {
//the version of sdk source used to compile your project
compileSdkVersion 23
defaultConfig {
//the minimum sdk version required by device to run your app
minSdkVersion 19
//you normally don't need to set max sdk limit so that your app can support future versions of android without updating app
//maxSdkVersion 23
//
//the latest sdk version of android on which you are targeting(building and testing) your app, it should be same as compileSdkVersion
targetSdkVersion 23
}
}