The gameplay in Theresia is very much like other point and click adventure games. You are given environments to explore (and explore them you must, with almost sickening detail) and hallways to traverse. Once in a room you can't really move at all, except to get a close up look at something. However, if you are walking down a hallway you do so with the d-pad (or the touch screen). Everything else, looking, touching and so on, is controlled by the touch screen. However, this can get a little annoying in that you have to click on the eye icon to look at things, but if you want to touch them you have to click on the hand. The back and forth can be a little jarring.
You really do need to look before you touch in Theresia. Almost anything can kill you (and you do have a life bar, so you have to be careful). Needles, knives and shards of glass are everywhere in this game world, and all of it wants to hurt Emilie. You do collect elixirs to replenish your health, but that doesn't mean you should touch anything without careful examination first. Sometimes, you can tell if something is going to hurt you (do you see something glisten? It's probably shards of glass).
Along the way you'll collect items to help you. You pick up plenty of items to help you solve puzzles. The game also usually lets you know if there is something important you have to do at a certain place by giving you little arrows to guide your way. This by no means makes Theresia easy, just a bit less difficult to figure out.