You want to have about half land half water. (the water needs to be dechlorinated.)
you can feed them aphids, (from the garden) wingless fruit flys (avalible from the pet shop, culture your own my putting small peices of bannana and apple in the tub) and will also eat daphnia (a type of aquatic micro organisim) but daphnia should just suppliment the diet because some juvenile newts won't wan't to get in to the water.
the tank should be at a good size about two feet long for two adult newts. on and a half feet for just the one. they will need a mesh lid on their tank other wise they can escape.
Thats just how I keep mine some people do it differently.