Another important thing is when launch the SDK manager you launch it as Administrator.
After the you will see following window.
Here we have that choose packages to install. Click cancel button.
Then click to Available Packages and scroll down Android Repository. Here we can see each API versions. We can download the SDK for that versions. Now I recommended if we have the time, download everything in this folder.
To keep it simpler I'm just going to download the SDK for Gingerbread.
Now you know it doesn't say Gingerbread here. That because you need to actually learn which version numbers represent with SDK.
v1.5 - Cupcake (Released on 30-04-2009)
v1.6 - Donut (Released on 15-09-2009)
v2.0/2.1 - Eclair (Released on 26-10-2009)
v2.2x - Froyo (Released on 20-05-2010)
v2.3x - Gingerbread (Released on 06-12-2010)
v3.x - Honeycomb (Released on 22-02-2011)
v4.x - Ice Cream Sandwich (Released on 19-10-2011)
Now another thing really important to download of the samples for each API versions. These contains some great demos created by Google. So select the option for download "Samples for SDK API 10, revision 1". Then click "Install Selected". Another popup box ask you to verify Package description and license. Select Accept all and choose install.
After download the updated SDK tools and samples close the window.
You can check installed packages.
It will show Android SDK tools, SDK Platform tools, SDK Platform Android2.3.3 and Samples.
You have downloaded everything need to start developing Android apps