SYSIBM is a schema - every (DB2 LUW) database has its own set of catalog tables. (In DB2 zOS its one set of catalog tables per instance - "database" has a very different meaning.) These tables are used to store a variety of system related information, including definitions of items created by users. Apart from some specialised information, no information in them is stored by INSERT or UPDATE statements.
Why would you want to create your own catalog tables? What do you intend to store in them?