When someone says, "it's all good," they are typically expressing that everything is okay, there are no problems or issues to be concerned about, and there is no reason to worry or be upset. It is a common informal expression used to convey reassurance, a lack of any negative feelings or conflicts, or that there is no need to be upset or troubled about a particular situation.
For example, if someone apologizes for a mistake or inconvenience, the response "it's all good" implies that the person who was affected by the mistake does not hold any hard feelings and forgives the person who made the error. It's a way of letting the other person know that there is no lingering animosity or negative emotions about the situation.
"It's all good" can also be used more broadly to convey a positive outlook or to reassure someone that everything is well in general. It is often used in a casual, friendly, and relaxed manner in everyday conversations.