After you are done with installation of Android SDK on Windows 10, you must set the ANDROID_HOME environment variable to point to the Android SDK installation directory.
To set up the Android Environment variable on Windows, you first required to have Android installation path with you.
By default it should be similar to this C:\Users\UserName\AppData\Local\Android\Sdk. If you are not able to find AppData folder you can follow this article.
Steps to set Android_Home Environment Variable path
Step 1: Open Control Panel -> System
Step 2: Click on Advance System Settings
Step 3: Click Environment Variables on System Properties Dialogue
Step 4: In User variables or System Variable section, click on New button. [Note: System variables are shared for all users, but user variables are only for your account/profile.]
Step 5: In New User Variable dialogue, Enter Variable name as ANDROID_HOME and Variable value as C:\Users\goswa\AppData\Local\Android\Sdk [Use your path here] and Click on OK button
Step 6: Select on Path variable in User or System Variable section and click on Edit or you can double click on Path variable as well.
Step 7: From Edit environment variable dialogue box, Click on New and enter path for platform-tools and tools.
Step 8: Go to command prompt and type adb. If everything successful you will see below output.
Note: You may need to open a new command prompt if you are getting command not found after setting environment variables.