What is the output of:
echo $PATH
?
That *should* include your home+abin; if not, then the AFNI binary directory hasn't been added to your path.
Note that if you have just done the setup, you might need to open a new terminal (or source your shell's RC file) for the change to take effect.
Try typing
echo $0
to see what shell you are using.
If the result of that is "bash" or "-bash", then type:
source ~/.bashrc
and now see if typing "which afni" produces a result (meaning that your AFNI binary directory is in your path.
If the result of "echo $0" is "tcsh" or "-tcsh", then type:
source ~/.cshrc
... and see now if "which afni" produces a result.
--pt