The copy of Kermit that RUCS distributes is configured for the default communications port, COM1. Follow the login instructions provided with your account. You are instructing the remote host's Kermit to send you a file. You must also instruct your local PC's Kermit to receive that file. Then press the letter c.
Type receive to receive the file from the host system.
A status screen will tell how much of your file has been transferred. If there are other files you want to transfer, then repeat the sequence, beginning with send filename, as many times as is necessary. Files that you have downloaded will be stored in the same folder as your copy of MacKermit unless you select a different target directory. When you download a file, you are actually making a copy of it. The original is still on the remote host.