AND, OR, NOT

OR: show a group if ANY of 2 conditions is true

Form:

[checkbox choice "first choice" "second choice" "third choice"]
[group g]you have checked first OR second choice[/group]

Conditions:

show [g] if [choice] equals "first choice"
show [g] if [choice] equals "second choice"

AND: show a group if 2 conditions are both true

Form:

[checkbox choice "first choice" "second choice" "third choice"]
[group g]you have checked first AND second choice[/group]

Conditions:

show [g] if [choice] equals "first choice"
     and if [choice] equals "second choice"

NOT: show group if a condition is false

You cannot invert a conditional statement.
There’s no such thing as a hide [group] if condition.

So, if you want to say something like:
hide group if X equals Y,

you will need to express this as
show group if X not equals Y

Form:

[checkbox choice "first choice" "second choice" "third choice"]
[group g]You have NOT checked the third choice[/group]

Conditions:

show [g] if [choice] not equals "third choice"