The first phase of orthodontic treatment with braces is levelling – correcting rotated teeth and teeth that are out of line vertically. Lining the teeth up requires space. This can be gained by expanding the dental arches or the jaws, or by taking teeth out. With expansion, the archwires pull the teeth forwards and outwards to find room. Sometimes this creates even more room than is needed, and gaps appear between the teeth. They will of course be closed, but this happens at a specific stage of treatment, not straight away. You may have to put up with some gaps between your teeth for a while.
This answer is for general information. Your own case needs an examination by an orthodontist.