We've put together some answers to often asked questions - you can find it in the Umbraco 8 - FAQ article.

Make sure to give the installation instructions a read.

Check the free foundation videos on how to get started building Umbraco sites.

You'll find our über active community working hard to help each other at Our Umbraco: https://our.umbraco.com

Make sure to read the upgrade instructions before you attempt an upgrade.

We're happy to help you with any problems you encounter, so please report them in the issue tracker and mention you're using version 8.15.3.
Do a search first though, if the issue already exists, give it a "thumbs up".

The source for this specific release is available for download from the repository (click the "ZIP" button).