As Asfouts says, there is a Cynops section where you should find helpful threads, but mainly look in this (Help) section. Many people experience similar problems with newts from pet shops.
One day without food is not really an issue - they will take some time to adjust and recover from transport, pet shop care etc. You need to make sure conditions are good for them - cool cycled water (ideally under or around 20℃) with no or very little movement, lots of plants with some floating ones, some hiding places. They should really be aquatic as adults so if they are staying on land for extended periods, something is usually wrong. Regarding feeding, try earthworms, they are very nutritious. You could also try lesser waxworms, live bloodworms etc. If they are on dry land, put the food near their hiding place and leave them to it (go away and turn the lights off if you can - that sometimes helps).
If you offer anything in water, make sure you remove it soon if it doesn't get eaten, otherwise it will decompose and mess up water quality.
Also make sure you have a 100% escape-proof lid.
Do as much reading as you can to understand what the newts need:
http://www.caudata.org/cc/articles/articles.shtml
http://www.caudata.org/cc/species/Cynops/C_orientalis.shtml
http://www.caudata.org/cc/articles/firebelly.shtml