If you've already installed SharePress, skip to Creating Your Facebook Application.
SharePress is available through the WordPress plugin directory.
Log into WordPress, and in the menu, mouse-over Plugins and click on Add New.
In the search box type "sharepress" and click Search Plugins.
Locate SharePress in the search results, and then click Install Now
Next, most users will be asked to supply their FTP hostname, username, and password. WordPress uses these to facilitate installing the plugin's files from their directory - SharePress is not capturing this information (in fact at this step, SharePress isn't even installed yet).
After installing, you will be asked whether or not you want to activate the plugin. Answer, "Yes."
Creating Your Facebook Application
Open a new browser tab or window, and visit the Facebook Developer's dashboard.
Then click Create New App
Next you'll be asked to name your application. I suggest you name it after your blog instead of calling it "SharePress" as many people do the latter. You'll also need to choose a namespace, but SharePress doesn't care about the namespace. In both cases - the name and the namespace - you'll need to choose something unique. You can leave the Web Hosting option unchecked.
Set the App Domain to the domain name you see in your Web browser when you're in the WordPress admin.
Scroll down, click the Website option under Select how your app integrates with Facebook, and in the field titled Site URL enter the URL of your WordPress site's home page.
Before leaving this screen, write down your App ID and App Secret - you'll need them in a moment.
Then click Save Changes
Return to your WordPress site, mouse-over Settings and then click SharePress.
Here you'll want to enter your Facebook App ID and Secret.
Then click Connect.
Barring unforeseen Facebook nonsense, the next thing you see should be a screen on Facebook, asking you to authorize the app you created above to access your information on Facebook.
Click Allow. Again, barring unforeseen Facebook issues, you should be redirected to your WordPress site and the SharePress settings screen.
Configure SharePress to your liking, click Save Settings, and you're done!