When you type code into a new program, remember to save it to a file before trying to run it. Usually it should have the .o2bas extension name but .bas will also be recognised.
In the ScITE IDE:
F5 will execute the program directly.
F7 will compile it and
Ctrl-F7 will both compile and emit a machine script/assembler listing into the lower panel.
If the program has an error in it, it will not execute. To get details of the error try compiling with F7 and the error will be reported in the lower panel
print "Hello World!"