To understand as something new, you have to use the exact verb form of the command, like this:
Understand the command "throw" as something new.
For the other understand lines, you don’t put the verb in brackets; that’s for the noun and second noun. So you’d write:
Understand "toss" or "lob" or "chuck" as "throw".
Understand "throw [something preferably held] at [something]" as tossing it at.
Understand "throw [something preferably held] [direction]" as tossing it at.
Tossing it at is an action applying to two things.
carry out tossing it at:
Also I think that if you want to allow tossing it at to apply to directions, you need to say “…applying to one thing and one visible thing,” because directions are never touchable.
Hope this helps!