If you have to repeat many times the same commands (this could be a complete calculation or just setting your system), you will appreciate the possibility to write macros.

A macro file is simply a text file containing the instructions you want to place in it, it will be clearer in the following example:
This macro defines the system for a 20/25 austenitic stainless steel, the phases I want to keep and the composition of the steel:

multiphase
define sou plus sub_sgte !
define sy 'Fe,Cr,Ni,Mn,Mo,Si,Nb,Ti,N,C' !
class abs p(*) no p(FCC_A1,BCC_A2,M23C6,NNb,CNb,NTi,CTi,SIGMA,M6C) !
set w 100 !
set w( ) undef 20.28 24.95 1.00 1.50 0.41 0.26 0.05 0.167 0.06 !

Using a text editor, save these commands in a text file that you call nf709.mac (for example; note that the extension could be anything).
Then call it from MTDATA:

WHICH MODULE ? '/huge/users/thomas/mtdata/nf709.mac'