You're thinking VisualBasic which has more bells and whistles like "PRIVATE SUB CMDHELLO", but none of that existed in the original BASIC of which SmileBasic is based on. Just the good o' fashioned PRINT "Hello world" (or ?"Hello world" like Keiren said). Type these in EDIT mode though, not the DIRECT mode in this screenshot.
In EDIT mode, also try this (as introduced in the Japanese homepage):
ACLS
XSCREEN 4
SPSET 2,501
WHILE TRUE
TOUCH OUT J,X,Y
IF J THEN SPOFS 2,X,Y
WEND
After you're done, press START, and try sliding around the touch screen.