From the upload page click Choose File and then locate the file you previously saved and upload it. Once uploaded and installed you have the option to activate the plugin immediately which you want to do by clicking the Activate Plugin link.
Once Welcome for Church is successfully installed you want to take a moment to activate your license for it in WP for Church Sidekick so that you receive updates and important notices automatically. You need to have Sidekick already installed and your licence key from your WP for Church account page.
To register your license simply navigate to WP for Church > Manage Licenses from the admin panel. Copy and paste your license key in the appropriate field and click Save License Key Changes.