You may have two problems. The only way water generally leaves the bowl is when you flush or it has a leak. That generally means a defective bowl. Water leaking from the tank is usually the flapper valve. Make sure that the chain is adjusted properly (i.e., it isn't too tight and not letting it close fully or too long, and getting caught underneath it). Also, make sure that the lever is not sticking or rubbing on something that prevents the flapper from sealing. Then, make sure that there's no crud caught on the seat where the flapper valve seals. If all of those look good, then the flapper may be defective. If you assembled the toilet, make sure that the flapper is installed properly. If there are lugs on the tower where the flapper attaches, and the flapper has a ring that goes around the overflow tube, cut out the ring and only use the lugs. If you use both, it almost never seals as it tends to warp the thing.
If the flapper valve is sealing, the assembly that that seals to may not have been tightened. That usually means taking the tank off and tightening the big nut on the bottom of the tank.
Note, the level in the bowl may take a moment to stabilize, but after that, unless it sits for a long time and evaporation lowers the level, or pets drink from it, it should not drop.
