If you have crooked teeth and/or a misaligned bite (an underbite or overbite), there are a variety of treatments that can help straighten teeth, including braces and retainers.
The dentist will ask questions about your health, conduct a clinical exam, take impressions of your teeth, take photos of your face and teeth, and order X-rays of the mouth and head. An appropriate treatment plan is made based on analysis of the gathered information.
In some cases, a removable retainer will be all that's necessary. In other rare cases (especially when there is an extreme overbite or underbite), surgery may be necessary. In most cases, however, braces will be needed*.
* Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner.