Here is a simple step by step guide that will help you to install ADB on your Windows computer. First, download Java SE SDK (link). Get the app by clicking on the first icon (which will take you here). Now, download Android SDK and extract its contents. Open the folder and start SDK Manager. From the list of packages, double click on USB Driver Package revision. You may deselect all the items except the USB Package in case you are on a slow Internet connection. Click on “install”.
Now, on your phone, go to settings > applications > development and turn on “USB Debugging” mode. Connect your phone via USB to the PC. You will get an error saying that the Device driver software was not successfully installed. Ignore it and open device manager (Start>Run>devmgmt.msc). In the device manager, expand “other devices” – here you will find your phone. Right click on it and select Properties. Click on “update driver” and then “Browse my computer for driver software” and then select “Let me pick from list of device drivers on my computer”. Click “next”>”have disk” and browse through and find “android_winusb”.
This will install drivers for your Android phone / tablet. That is it.