Generally we tell apart fruits and veetables based on how they taste and how they are eaten or cooked. We think of fruits as foods that grow on trees, taste sweet, and can almost always be eaten without cooking. We tend to think of vegetables, as foods that grow in or near the ground, and are eaten after cooking, sometimes can be eaten raw too.
According to science, a vegetable is any part of a plant that can be eaten, like leaves, stems, or roots. So vegetable is any edible part of a plant. A fruit is also the edible part of a plant, but refers specifically to the edible part of a plant that has come from its ripe flower. The major fruit and vegetable difference is that most of the fruits contain seeds, which are capable of developing into new plants and vegetables lack seeds (there are exceptions to this though).