This is figurative language. Imagine the literal image - someone feeding a baby with a spoon. What does that normally look like? The spoon is usually smaller than normal, the food is usually simple and easy to consume, the one feeding usually has to encourage the baby to eat- sometimes making special noises or funny faces as they try to urge the baby to accept the spoon.
Now imagine the figurative image. The one doing the spoon feeding is trying to convey information to someone that is having a difficult time understanding or accepting that information. Therefore they must break it down into smaller bits of simple information and encourage the one being fed the information to accept it.
Spoon-feeding refers to feeding someone difficult or complicated information, in such a simple manner that even a baby could "swallow" it.
The phrase spoon feeding means to feed someone, such as a baby, with a spoon. Babies aren't able to feed themselves with a spoon so it is expected that an adult feed them until they reach the age of development when they can feed themselves independently.
The word spoon-feed can also be used to describe what is done when information is given to a person without them applying any effort. When a person is spoon-feed information the information is usually given to them slowly, to ensure that they consume all of the information given. In this definiton of spoon feed, the person is seen as spoiled, babyish, and coddled.