To install Webex, you will need to be an Administrator for your Webex account and must be using the Webex Event Manager.
Webex URL, Site ID and Partner ID can all be found at Site Administration > Site Information in your Webex account (https://bedrockdata.webex.com/wbxadmin/default.do?siteurl=your_site). Do not include https:// in the url.
Webex ID is simply your username and password is the password you use to log in with this user. As noted above, you must be an Administrator.
For Site ID and Partner ID, you may need to contact your Webex Account Manager to obtain these IDs per the following Webex API FAQ.