The basic hx509 cerificate object in hx509 is hx509_cert. The hx509_cert object is representing one X509/PKIX certificate and associated attributes; like private key, friendly name, etc.
A hx509_cert object is usully found via the keyset interfaces (Certificate store operations), but its also possible to create a certificate directly from a parsed object with hx509_cert_init() and hx509_cert_init_data().
See the library functions here: hx509 certificate functions
1.9.1