Gums can be swollen short term or long term. If you have an area of gum that suddenly has some swelling there could be a number of reasons. Frequently there is some food debris (popcorn hulls, seeds, and meat are often the culprits) caught in the area between two teeth. The first aid measure if your gum is swollen is to gently brush and floss the area, trying to dislodge any debris. Sometimes it helps to tie a knot in the floss and then drag the knot back and forth through the swollen area to drag out any debris. Also helpful is to get a glass of warm water, mix in a teaspoon of salt, and then rinse vigorously with the entire glass to try to flush out any debris. This can be repeated several times a day.
If the swelling is long standing, persists, or increases you should see your dentist who with the aid of an x ray and tests will determine the cause and prescribe the proper treatment. The dentist will determine whether there is infection present and whether to prescribe an antibiotic. If you have frequent recurrences or a number of teeth that have swollen gums it is likely you have periodontal disease and require diagnosis and treatment of your condition.