basic.at          basic functions
groups.at     	  defining groups
misc.at       	  miscellaneous useful commands
lietypes.at   	  lets you say C4 instead of "C4", and so forth
hermitian.at  	  functions related to c-forms and Hermitian forms
kl.at         	  Kazhdan-Lusztig polynomials
unitary.at  	  some unitary parameters
nilpotent.at	  for parameters related to nilpotent orbits
translate.at  	  functions related to translation {experimental}
sort.at		  functions for sorting parameter lists in various ways
test.at		  functions for testing the algorithms in many cases
iterate_deform.at algorithm for deforming nu to 0, now built into Atlas
sp4.at        	  some stuff tailored to Sp(4,R)
test_unitarity.at tests of unitarity

K_types.at	  branching modules to K
LKT.at		  lowest K types
modules.at	  polynomials of parameters labelled by their interpretation
...		  (for more see scripts.help)
all.at         	  include numerous files to have many useful functions at hand

To load basic.at, for example, do:

<basic or <basic.at

Every file will also load all the files on which it depends.
Probably you should just do:

<all