I don't use DASM on Macs only on PC. On the PC its a command line tool so I assume its the same on the Mac. In which case you need to tell it what to assemble.
Ok, I'll try that. Thanks for your help! (if you couldn't already tell, I'm quite a newbie).
No worries. This is actually a common mistake with newbies. It would be nice to have a 6502 assembler that runs in a GUI mode, but the few I'm familiar with use a CLI (command line interface) mode, so you can't just double-click or execute the assembler-- you have to type a command line that indicates the source file to be assembled, along with any other parameters. The DASM.TXT file should give you an explanation of the different parameters that are available. One thing you need to know-- if you want to assemble a file for the Atari 2600, be sure to include -f3 in your command line, so the output file will be in the "raw" format.
Sorry for replying late, but thanks for the help!