Option 1
for windows
Right click on My computer -> properties -> Advanced system setting -> Environment Variables
Now Edit Path on system variables to
;/yourSdkHome/tools;/youSdkHome/platform-tools
Option 2
In Windows machine, Open Command prompt and enter each of this commands one by one
set ANDROID_HOME=**C:\\android-sdk-windows**
set PATH=%PATH%;%ANDROID_HOME%\tools;%ANDROID_HOME%\platform-tools
In MAC Machine, open Terminal and enter these one by one
export ANDROID_HOME=/<installation location>/android-sdk-macosx
export PATH=${PATH}:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools
Note - C:\\android-sdk-windows
should be replaced by the path of Android SDK in your machine.
<installation location>
should be replaced by the path of Android SDK in your machine.
Example
in MAC machine, if install location is ~/adt-bundle-mac-x86_64/sdk
first line should be
export ANDROID_HOME=~/adt-bundle-mac-x86_64/sdk