Installing Movable Type Plugin
Now that you have downloaded the Movable Type plugin you need to install it.
Load Extensions Install Screen
Choose the Extensions > Install/Uninstall menu item to navigate to the plugin installation screen.
Click on "Choose File"
Select the plg-xmlrpc-movabletype-2-3-3.tar file that you downloaded. Next click the Upload File & Install button.
If all goes well you should see the Install Plugin Success message along with some details about the plugin.