It is not clear what is exactly in the files but might guess from the names:
- X509Cert - probably the leaf certificate, i.e. the server certificate
- interCert - probably the intermediate certificates
- rootCert - the root certificate which should not be included in the server configuration. If this is no public root CA it have to be installed as trusted on the TLS client instead
- PKCS7Cert - a container with probably all of these together in PKCS#7 format. See also What's the difference between X.509 and PKCS#7 Certificate?
I'm guessing one is a private key
Probably not. The private key is usually created by the one requesting the certificate and kept private. Thus if you created a certificate signing request and got these files in response you should already have your private key. If not they might have included the key in the X509Cert file and/or the PKCS7Cert.
I got it through the company IT department, they didn't give me any documentation, just those files.
I'm not sure how processes in your company work. But where I work the usual procedure is to ask the ones you got the files from on what to do with the files.