Commands

RUN - run the program that is tokenized in the runner
CONT - continue where the program exited (at a STOP instruction or if user hit Esc)
LIST - change screen mode to Program Listing
NEW - clear the program from both the Program Listing and runner
OLD - restore the program after NEW
DGNS - print all built-in designs
Question mark: enter an expression following ? to see its value.
By entering a programming instruction, you add a line to the end of the program.

[Csaba Skrabák]

By entering a programming instruction, you add a line to the end of the program.

You'll often get INSTRUCTION EXPECTED ERROR after entering text to the READY prompt. It is because the emulator tries to add it to the program, and it fails parsing as an instruction. The error message misleads a little because the input may be any command, not necessarily instruction.