If you had just a little piece of dental bonding (plastic composite filling) chip off of your teeth, then it can sometimes be repaired just by adding some more bonding over the chip. How well this repair can be done may depend on how long ago the original bonding was placed, what particular material was used for the original bonding, and your bite or occlusion (which may be why the bonding broke in the first place).
However, if your dentist tries to repair the bonding (without removing the entire bonding and starting over from scratch) you should be aware that he will most likely tell you that there is no guarantee how long a repaired bonding will last. There are just some limitations with the ability to bond new bonding over old bonding.
The most predictable way of repairing a broken bonding is to completely remove all the old bonding first and then place a completely new bonding.
Usually we will try to repair the broken bonding first, and if that fails then replace it with a completely new bonding.
Regarding your question, "how will the tooth look underneath", that depends on how much tooth broke off before the original bonding was placed.