Let's say you ask the administrator of an FTP server for a certificate. This certificate must be registered with the FTP server; presumably, the administrator will have done this by the time the certificate is delivered to you. The certificate will likely be delivered to you either in the form of two ASCII files with extensions .crt and .key (or perhaps .cer and .key), or one binary file with an extension .p12 (or perhaps .pfx). Place these file(s) on the computer running MOVEit Central. If you are using a network file transfer mechanism to transmit the certificate file(s), be sure to choose the proper ASCII vs. binary transfer method.
Regardless of the file type, there will also be a password, which you must know before you can use the certificate.