There are two types of springs that can be placed in the mouth along with braces – opening springs and closing springs. When the spring is shorter than the distance between the two brackets its ends are attached to, it pulls those brackets, and the teeth they're on, towards each other and reduces the space between them. When the spring is cut longer than the space between two brackets – it's usually threaded onto the archwire – it pushes the teeth apart and creates space.
This answer is for general information. Your own case needs an examination by an orthodontist.