From your link, your bike has Tekro HDC Hydraulic brakes.
If you do a google search, there is a video (made by Tekro by the looks of things) which talks about how to replace pads on these brakes.
I suggest you watch this video. If you understand it, and feel comfortable doing what it suggests, take the pads out and examine them. Don't buy any replacements just yet - fingers crossed, simply taking the pads out and putting them back in might solve your problem. Also read up on the pistons, try to get an idea how they actually cause the brake to work, and satisfy yourself that all is well.
If you're not comfortable with any or all of this, take the bike to your local shop.
My first encounter with hydraulic brakes, I ummed and erred for ages because it was something new to me, when I finally found the courage it was quite a straightforward job - I did it in front of the laptop watching one of these vids, pausing it frequently so as lot to let them get too far ahead.