Very likely that the water is dirty. Goldfish are very messy fish that require far larger tanks than 10g. See this thread for why:
http://www.aquariumadvice.com/forum...uire-big-tanks-visual-perspective-265871.html
If the tank was not cycled before you added the goldfish, you're likely having ammonia or nitrite spikes that are at toxic levels, causing the fish to freak out and try to find a way to get to cleaner waters. It's like a human trapped in a room full of poison gas. If the tank was cycled, your nitrate levels are probably sky high due to too much bioload in too small of a tank.
Best next step: Return the goldfish to the fish store, do a large water change on the tank, and cycle it properly (if not previously cycled), then return to the fish store and pick out some more suitable fish. I highly recommend playing around with stocking plans in the stocking calculator on aqadvisor.com before buying any fish. It's not perfect, but it's a good sanity check that can help you direct your further research.
If you're not willing to do that:
Pick up a API master test kit to check your water parameters and do 25% water changes every half day until you can get down below 0.5 ammonia, 0.5 nitrite, 40 nitrates. Continue testing your water daily and do a 50% water change any time you go over those levels. Buy a 30g+ sized tank and start cycling it, and move the goldfish into that one once you get to 0 ammonia and 0 nitrites.
Leaving the goldfish in the current tank will result in a dead goldfish after a slow painful death
