First steps
Step 1: Launch
Once you have launched Butler you will notice that your menu bar has been populated by three new items: two icons and a Google search text field. (If you cannot see them, you might have run out of menu bar space.) All of these can be easily removed or moved to a submenu if you wish. If you're running Butler for the first time, Butler's main window will pop up, displaying its "About" section. The same happens after upgrading Butler to a new version.
Step 2: Configure
If you click on the little iMac icon in your menu bar you should see a menu called Butler; select this and then select "Customize configuration...". Butler's main window will open. You can configure everything to do with Butler from this window. You will see there are five icons at the top, representing the different sections of the window. Apart from the "About" section, which you have already seen (see above), and the "Help" button, there are three more sections.
The "Configuration" icon brings up the section where you can organize and set up all the menu bar icons and contents. There is a top-level item for each of the three items currently in your menu bar, as well as a section called "Hidden", which, surprisingly enough, is not visible. The procedure is the same for all top-level items. You can add or remove them, or items within them, and change orders and hierarchies via drag & drop.
If you click on the "Engines" button at the top, you will enter the section where you can configure all the search engines that can be used for searching the web from Butler. You will see there are already quite a few pre-installed.
Finally, have a look at the "Preferences" section. You will see several categories on the left and the options on the right. These options should be fairly self-explanatory; trial and error will be the best way to see what they do.
Step 3: Explore
Now just go ahead and play with your Butler. The default configuration contains almost all possible kinds of items, along with some comments. Thus, the best way to grasp what Butler can do is to browse through its menus. And remember you can set keyboard shortcuts (so-called hot keys) for anything, so you can use these to launch your favorite applications/files/bookmarks/whatever. But menus and hot keys are not the only ways of triggering actions with Butler. Don't forget to have a look at abbreviations, pop-up menus, hot corners, and events.