Beginner question: how to pause startup.int to see error messages?

[Edward Mendelson <em36@xxxxxxxxxxxx>]

I'm setting up a standalone (one-directory) XyWrite4-vDosPlus system 
that I hope to post when it's working correctly. What's stopping me at 
the moment is this:
When I start the program, a few error messages flash by saying things 
like "vDosPlus only" (though I am running vDosPlus) and something that 
may say "Command not found." How can I pause startup.int so that I can 
figure out which command is producing the error message?

Every schoolchild probably knows the answer, but unfortunately I don't.