Alli, the very first thing that comes to mind is that they are are "stretching" and exhibiting leggy growth, which usually indicates that they need brighter light. An east facing window would give good strong morning light. If it was outside in the shade, and you brought it in, that could also cause the leaf wilt and legginess.
The best "rule of thumb" for watering is to push your index finger down into the soil to the second joint. You can tell if the soil is really wet...too much water. If it is dry, time to water. This works with any actively growing container plant.
As for how to care for various container plants, you already have a great reference...
http://garden.org/plants/ The Plant database here at ATP.
Also, just enter the name of the plant with the words how to care for ( How to care for Oxalis triangularis) into the search bar. Just remember it is best to consult a couple or three sites when you do search. Usually these sites will give you info on what soil the plant needs. (pH...acid or alkaline, quick draining, coarse, nutrient rich, etc) the links below should give you some basics.
http://urbanext.illinois.edu/c...
http://www.finegardening.com/s...
http://www.finegardening.com/s...
http://houseplants.about.com/o...
http://www.gardeningknowhow.co...
I hope this helps.
