The first thing you will want to do is install the Install Manager. This will simplify the entire process, including installing new content in the future. You can download that here: http://www.daz3d.com/install-manager-info
NOTE: Mac Users, if you receive an error during download and install "identity of the developer can not be confirmed" You will need to go into your security settings and set your Mac to accept all applications.
Once you have installed Daz Install Manager, you will want to enter your account information (email and password). Once it has logged in, look under the Ready to Download tab. Locate "Daz Studio 4.8", check the check box next to it, make sure "Install after Download" is checked at the bottom of the window and click Start Queue at the bottom left. This will install Daz Studio. Once installed, you will see it listed under the Installed tab.
After Daz Studio is installed, you will need to install your content (figures, clothing, etc). Locate and check the boxes next to Genesis Starter Essentials, Genesis 2 Female Starter Essentials, Genesis 2 Male Starter Essentials, Genesis 3 Female Starter Essentials and Default Lights & Shaders. Click Start Queue.
Once these are all installed, open Daz Studio. There should be a launch icon on your desktop.
For additional help learning to use Daz Studio, please see our Quick Start Guide here: http://docs.daz3d.com/doku.php/public/software/dazstudio/4/userguide/start