To get direct responses to your sent messages you must use a virtual number or short code as the Sender ID.

One a recipient resonds there are several ways to view it in the application.

Activity Count

In the ACTIVITY section of your account click on the number representation of the number of responses from the Resp. column as shown below clicking on these will take you to the responses report for the message send.

Responses Tab in Report

In the Overview section of your account click on Report from Actions column as shown below and click on RESPONSES tab as shown below:

Activity Inbox

All responses can also be viewed from Overview > Inbox of your account as shown below: