Good and bad are not Platonic ideals. They are not things existing on their own in the world. Instead, good and bad only exist in relation to goals. Achieving a goal is good. Failure to achieve a goal is bad. [More discussion]
There is a hierarchy of goals. Most goals are actually sub-goals leading up to a higher goal.
There is a highest goal, which I call the root goal. It does not lead to any higher goal.
There is just one highest goal in all the world. The root goal is common to all living things. And non-living things do not have goals.
To define the root goal is tricky, but I generally say the root goal is to transmit your genes to future generations. [More discussion]
Just about everything people do is in some way an effort to achieve the root goal, ultimately. We have no choice but to pursue the root goal.
People's pursuit of the root goal is rarely explicit or conscious. People are usually unaware that they are pursuing the root goal.
People can't know for certain whether their actions are good or not, because they don't know the future. They can't tell whether their actions in the present will help or hinder their long-term achievement of the root goal. Therefore, morality is just people's best guess about what they think will work.
The root goal is open-ended! You can never achieve the root goal once and for all, but you must always keep striving.
When you say something is good or bad, you are indicating that you feel inclined to approve or oppose that thing. That's all it means! You feel inclined to approve or oppose something because you sense somehow that that thing either helps or hurts you somehow in your pursuit of the root goal.