difference between .tcl,.cc,.h,.tr

As far as ns2 is concerned, generally, the tcl file will contain the main simulation code. Sometimes, additional tcl files also can be used from the main simulation script.

The main ns2 simulator code itself was written in .cc, .h and tcl files. It means an ns2 object can be a c++ level implementation or a tcl level implementation.

Generally while doing a project on ns2, some of the packet level functionalities will be implemented in c++ code and those lower level function or classes will called/used from a tcl script.

Using an output file with extension .tr is a convention in ns2 – generally, those files are used to log some  event traces for further trace analysis.