Type commands in the screen above.
Try: PRINT "HELLO WORLD"
Try: POKE 53280,2 (change border to red)
Try: POKE 53281,0 (change background to black)
Try: PEEK(40960) (read ROM byte)
Try: 10 FOR I=1 TO 10
20 PRINT I*I
30 NEXT I
RUN
Try: LOAD "*",8,1 (easter egg!)
Try: SYS 64738 (reset)