To install Connector for Salesforce + Campaign Monitor, first you must have your own Salesforce app (or "org" in Salesforce terminology), which is Enterprise Edition or above.
You also must have appropriate system privileges to install and configure for the Connector. If you are a System Administrator for your Salesforce org, you're good to go.
The tasks for the installation and configuration require some knowledge on Salesforce administration. There are quite a few things to do before you can start using the Connector -- so please be patient and follow the instructions in the following document:
Connector for Salesforce + Campaign Monitor: Installation and Configuration Guide