Installing apk , adb command not found

1 Step If u have multiple emulator than close all emulator and open emulator by Window--> AVD Manger --> and select any one emulator on which u want to install apk and start that emulator by clicking on Strat

2 Step Open Command Promot and enter path upto folder Platform-tools of android sdk somethiing like cd C:\Program Files (x86)\Android\android-sdk\platform-tools if 64 bit other wise C:\Program Files\Android\android-sdk\platform-tools

3 Step adb install Path Upto ur apk means path in which folder u have put apk Example adb install C:\User\Download\facebook.apk

First add your Android SDK path like "C:\Android\android-sdk\platform-tools" to your OS path

Second use this command to restart adb:

adb kill-server
adb start-server