Yes. Most parents begin to feed babes at around 4 months. Gerber foods are fine. Usually start with cereal, then yellow veggies and then green and then others adding in one at a time a week at a time. Usually avoid fruits till later so as not to make "fruit" babies out of them. Start slowly and and add slowly. Breast milk is best still at this age and formula is fine.
Introduce baby food. For a four month old you should first start by introducing him to cereal. After the baby tolerates the cereal for a time you can then start the stage 1 baby foods. You can introduce one food at a time. To ensure that he doesn't have any food allergies, you do the same food for 2-3days. If no reactions occur (rash, hive, etc.) you move on to the next stage 1 food.