You will need 3 Data Points to connect your Authorize.net account via the Integrations Page. Here is what you will need
1) API URL
TESTING API Endpoint: https://apitest.authorize.net/xml/v1/request.api
LIVE API Endpoint: https://api.authorize.net/xml/v1/request.api
You can change this URL to switch between TEST mode and LIVE move with Authorize.net
2) Login ID
3) Transaction Key
Authorize.net will provide the last two values for you to copy and paste. Then your integration is live!