It'll be best to explain by showing you.
Script
#dynamic 0x900000
#org @start
lock
faceplayer
message @question
boxset 0x5
compare LASTRESULT 0x0
if 0x1 goto @yes
message @no
boxset 0x6
release
end
#org @question
= Does 2 + 2 = 4?
#org @yes
message @yestalk
boxset 0x6
release
end
#org @yestalk
= I thought so!
#org @no
= Yes it does! Are you stupid?
End Script
So what you have to do after 'boxset 0x5' is put compare LASTRESULT 0x0.
This tells the script to wait for your Yes/No.
Next is the if 0x1 goto @yes - I like to use @yes so you know what your pointing to.
compare LASTRESULT 0x0 and if 0x1 goto @yes
when using these if they player selects yes, the script will go to @yes. Try to think of this as a whole other script where you now have to put message @pointer and boxset 0x6 followed by release, end so your script doesn't crash.
but if they say no, the script will just continue, that is why I wrote out another message for the answer no.
followed by release, end.
Does that all make sense?