Android is a mobile operating system developed by Google, based on a modified version of the Linux kernel and other open source software and designed primarily for touchscreen mobile devices such as smartphones and tablets.
The Android Software Developer Kit, simply named as Android SDK, or ADB is what all the advance users of Android should have installed on their Windows running computers.
Below are the steps for downloading and installing Android SDK
Step 1: go to this link
Step 2: Click on Android "Download Android Studio" button
Step 3: Accept the agreement and click on button "Download Android Studio for Windows". [Download will start automatically]
Step 4: Start the installation by double clicking or clicking on Run.
Step 5: Click Next, and do not uncheck "Android Virtual Devices" checkbox.
Step 6: Change the location if you want to, otherwise let it remain default and click Next.
Step 7: Android Studio will be displayed in textbox. check "Do not create shortcuts" if you do not want shortcut and click install. [Installation will start]
Step 8: Click Next after installation complete.
Step 9: Click Finish and Uncheck "Start Android Studio" if you do not want to start Android studio right now.
Step 10: Launch Studio if not started earlier and click Next on Welcome screen.
Step 11: Select Standard on Install Type screen
Step 12: Select UI Theme
Step 13: Click Finish on Verify Settings page
Step 14: Downloading will start this will take time. Around 1-2 hours.