When you try to turn the steering wheel will it move at all? It should move freely with a little bit of effort. If the wheels are turned and the steering wheel is bound it will keep from turning the key. Turning the wheel hard away from the direction the tires are turned and gently turning the key might work.
It has already been mentioned Make sure your Vehicle is in park.
If the key is not working with one side flip the key over and try the other side. One side might not wear as quickly as the other.
try a different key (If you have one. If you do not Shame Shame on you)
Does the key in ign Buzzer ding when you insert the key?
Make sure the key is going all the way into the lock. Sometimes debris will keep a key from going all the way in.
If the key is worn at the shoulder or if the shoulder rest on the lock cylinder is worn, you may be able to turn the key if you apply ]u]slight turning pressure and slowly extract the key.
Apply a lubricant such as triflow into the lock. Insert and remove key a few times to help remove debris and lubricate the springs.
try jiggling the key while applying slight turning pressure
If none of that works call a locksmith. we have to eat too!
Hope some of that might be helpful.