To receive replies, you need to either have a Keyword or a Number active on your account. Once you have one of those, your contacts can reply to your messages or send you a message directly.
You can view messages up to 30 days after they’ve been sent or received. For messages received within and beyond this time period (up to 3 months), you can export an Excel file with different values included in the export. To go to your SMS & Voice Overview, select the option in the left hand column of your Dashboard.
Within that overview you can view your replies by selecting the ‘Received’ tab, and export them as you see fit under the ‘Export’ tab.