Hi S.,
Generally, the APA recommends starting babies on solids between 4 to 6 months. Though, nutritionally babies get all that they need from milk until they are close to a year so some people wait even longer. Food is not NEEDED. However, that said, it's an important developmental stage for them to begin exploring different tastes, textures, smells, and variety etc. So you could begin to offer foods (introducing something new every 3 days so that you can monitor for allergic/gas reactions).
Many people will tell you that cereal is the first food they should have. But it is in fact not true. The APA says that after 6 months, most foods are safe for babies as long as they don't pose a choking hazard. It's good to delay foods that are high allergy rates until they are a year (eggs, nuts, fish, and honey b/c of botulism spores).
Also, don't feel restricted by using a spoon. And you don't have to use store bought baby food which is expensive. One of my twins loves to eat with her hands. The other loves the spoon. They are 6 months old and they eat about 3 to 4 tablespoons of food in the AM and in the PM. I generally give it to them after their milk, and they tend to take a shorter milk feeding the next time a few hours later, but not much shorter. I give them sweet potato, squash, banana, avocado, pureed corn or peas, pear. If they are not loving it, sometimes I mix with banana or breastmilk to sweeten it up.
I *love* the book: Child of Mine: Feeding with Love and Good Sense. It has many really good chapters about feeding that are super practical. Great book, and helpful for feeding through the toddler years. It is cheap if you buy it used on Amazon.
Good luck!