Construction interface problem

[Construction interface problem]

can someone please dumb this down for me i am not a computer wise guy i don't have a clue where to put this and i don't have a clue on what a init means please and thank you

[Is it possible....]

Is it possible to use Addons in ArmA 2 demo version i ask because that all i can get right at the moment and i want to experience atleast a taste of the full retain beside i don't have a good enough computer for the full version yet if someone can send me the links or a list of objects and where i may find them i would greatly appreciate it. thanks