Children first learn to take things with their hands and then acquire the skill of using more complex utensils. Thus, it is natural that at first they do not know how to use the fork or spoon and prefer to take food directly with their hands. Is that if using their hands they get what they want, why would life get complicated with those strange gadgets called cutlery?
Every child has their times; My daughters have had a hard time not eating with their fingers. At four years they already had enough agility to learn certain cutlery use rules.
At first, your child is likely to get dirty more than usual or spill much of the food, but insist. To motivate you you can buy some special cutlery, appropriate to your measurements, and allow you to help yourself by pushing the food with your free hand. Later you can show him how to use a piece of bread to help himself.
You will see that at first he takes the cutlery with his whole hand, closing his fist to hold them better. It is normal; Show him how to do it and invite him to try. He will often forget and return to his fingers, but over time he will get used to doing it well. Little by little you can tell him that each cutlery has a stipulated function: the soup is best eaten with the spoon, the fork is useful to prick the tortilla and the knife is used to cut the meat. Do not introduce all the utensils at once: do it one by one, first the spoon, then the fork, finally the knife, and help prepare easy-to-handle food with each cutlery.
You will probably refuse to use the fork once you have learned to use the spoon. Think that for you the cutlery are tools of habitual use and you are used to handle them: it costs a lot this whole process, be patient.
Tell him that it is dangerous for him and for those who share the table that plays with the cutlery: he can hurt himself or others because they are hard and pointed. Also, if you shake them, the food will end up scattered all over the table, even on the floor! The cutlery serves to eat, therefore, you should not play with them.
