I grubbed off 200 square feet of sod to put in new planting beds. I sent the soil to the U Conn soil lab and was quite surprised to learn that the soil had an adequate amount of organic matter and "decent" levels of major nutrients: nitrogen, phosphorous, and potassium. I could have grown low demand crops like greens in that soil if I needed to. However, this is a hobby, and I eagerly added grass and leaf mold to the beds to enhance them. They sat from October to June and had nice looking soil to start crops in the spring.
A new gardener needs to add organic matter and nutrients to the soil for healthy plants and adequate yields. One could go to the garden center and buy a fertilizer that will perform well for the season. Good results would be obtained. Much could be added to this thread to explain soil fertility, nutrients, and organic material. However, my simple advice is to acquire a complete fertilizer with major and minor nutrients and I have a definite preference for organic fertilizer because the soil microbes stay healthy and the nutrients are released throughout the season.