Hi Welcome to Drupal stackexchange
If you want to get started on theming.
You should Go after some of the famous base themes like Fusion, Zen, Omega
I see fusion as very easy.
If you've ever installed a Drupal theme before, you'll find that
installing Fusion is just as easy. And if you haven't, don't worry:
You'll still be fine! There are five simple steps:
Download the Skinr module (the 1.x branch, as of March 2010), which
gives you access to many of Fusion's unique features Download Fusion
Enable the Skinr module Enable and set a Fusion subtheme (such as
Acquia Prosper or the included Fusion Starter) as your site's default
theme Give yourself permission to access Skinr's controls If you’re
not the site's "super user" (that is, the person holding the first
account created when you installed Drupal), you (or someone with
sufficient permissions) need to explicitly allow you to use Skinr's
features. Go to the user permissions page (e.g.
http://www.example.com/admin/user/permissions), scroll down to the
"skinr module" section, and check all boxes under your user role.
Here is a how to in creating a Fusion Sub theme