SharePoint Desiger is the best tool for user-experience customization of SharePoint sites, at least for those who aren't fluent in code. This software is available for free on the Microsoft website and comes pre-packed with most SharePoint deployments. This article walks you through the basics of using that software.
During the installation process of SharePoint Designer, the default settings (for the installation, maintenance, Microsoft updates, and so on) are typically preferable. Do not choose non-default options unless you're confident about what those changes will mean. If you have any problems with locating, downloading, or installing SharePoint Designer, the best way to troubleshoot is to refer to the Microsft site. Once you have Designer installed, you're ready to move forward with this article.
Setting Up a Base Template
To ready a template for your SharePoint sites, you will go to File → New → Web Site. While there are multiple options available here, the best path is to choose "SharePoint Templates" and select one of the blank basic sites you see on this page. While they lack dynamic content and web parts, those pieces can be added later without difficulty as the templates are pre-built in the ASP.NET framework that allows for such dynamic elements. Unless you have strong reasons for doing so, importing a site at this stage is not recommended.
Connecting to Your Hosted SharePoint
To synchronize with your hosted SharePoint, simply enter the URL of your SharePoint into the "site location" box and click "OK." From here, you will be asked to input your SharePoint credentials (i.e., username and password). Once you have done so, Designer will automatically make the necessary synchronizations.
Using the Interface
The SharePoint Designer interface is designed to be intuitive for users, especially those familiar with the Microsoft Office suite. While a great deal of good comes from simple experimentation, there are dedicated guides to navigating Designer, with the most prominent coming from Microsoft itself.