1. Where can a merchant find Magento extensions?
Magento hosts
Magento Connect, which is a repository of free and paid extensions for Magento. https://www.magentocommerce.com/magento-connect/
2. What are the two ways of installing an extension in Magento?
Installing via MagentoConnect
Manually copying files to the filesystem
If the extension was obtained directly from a vendor or written yourself, you’ll need to copy the extension into the correct Magento source directories.
3. How can a Magento Admin user disable an extension using admin functionality?
In the backend, navigate to `System -> Configuration -> Advanced Disable Modules Output`
Installed modules are shown and individual modules can be disabled here.