Typically that's how it works. Did you buy the bike from a local dealer? If so didn't they go through the operation of the bike?
Here is a link to a owners manual that explains the operation of a bike very similar to yours. If you go to Giant's site they have a customer support link as well.
+ and - buttons helps to increase (+) and reduce (-) the level or the power of assist you need when you are cycling. Just play around and you should be ok.