There are generally two ways carbohydrate energy is stored as fat.
First, glucose may be directly pushed into adipose cells (fat cells). This is not actual storage as fat, but it might as well be.
Secondly, liver glycogen may become full. The liver is the regulator of blood sugar --- excess blood glucose is sometimes stored as liver glycogen. This is used later in the event of low blood glucose. When liver glycogen becomes full, the liver converts glycogen energy to fatty acids and sends it into the blood stream. This is why a high carb diet still results in fairly high blood fatty acid levels.
Insulin causes fatty-acids in the blood to be stored in adipose tissue. Insulin is secreted then blood glucose rises above baseline. This means that the ingestion of carbohydrate causes insulin to rise and causes fatt-acids to be stored in fat cells. This continues until blood glucose returns to baseline. At this point, all of the excess blood glucose has been stored in either muscle cells (as muscle glycogen), fat cells, or liver glycogen stores.
Conversely, when blood glucose falls below baseline, fatty-acids are mobilized from fat cells and liver glycogen is used to replenish blood glucose.