The OVF will package all of the virtual machine files into a single folder. It will have an OVF descriptor file, which will have an extension, .ovf; a manifest (.mf) file; the virtual disks; and certificates, if any. 

The manifest file contains the SHA1 digest of all of the files in the package. The OVA is simply a TAR file with the OVF folder packaged inside it. The .ova extension can even be changed to TAR and have its content extracted by an un-archiver such as 7-Zip.