I am not native speaker but will try to explain. Normally 好的 is just same as 好 but 的 helps you to emphasize 好, but 好了 is totally different, it means you just finished something (doing, talking) or gonna finish and gonna switch your talking, doing and etc to new activity, topic etc. Example: - 好了 我结束了 咱们出去走走吧 -好的！走吧 对了 can have two meanings. One is when 了 helps you to emphasize that someone is correct NOW (maybe opposite to what he said lately) . The second meaning of 对了 is close to the english "BY THE WAY" (probably) using before you re telling someone thing that you forgot to tell or supposed to tell before 对了 你还没给我钥匙 ! 对了 你今天不回去吗？

Hi,左一老师, I want to say hi to you because you claimed that you were living in my hometown Dongguan. plus I want to learn English from you. Mike's answer is correct but I want to clarify it. This is a simple grammar question of Mandarin. when you search mandarin grammar chart you would find a lot of materials. 1. something(noun/verb) +的 it is a function word that indicates this as an adjective word.. . 2. something(verb)+ 了， usually for action in the past that have been completed. but here for 表示感叹语气 modal particle。如：好了！别闹了！ scenarios: A。你去跟左一老师学英文吗？ B。是的，（ answer yes）。 A，你去学英文吧。 B。好的。 A , 对了，你的coronavirus outbreak怎么样？（对了是一个转折点，transition word) B，好很多了。 A。好了，你要去睡觉吗？ B。好的（yes) 和对了都可以，（you are right and yes they are same) A. 好了（okay），我也去学英文了，再见。 B。好的（yes)。再见。 Regarding to 对的(you are right)and 对了(by the way)。usage it is same with 好的，好了。

好的 can be used to decribe an agreement of a plan, a sugestion, something that has not happened yet. 好了 means, it's enough, something is done, something doesn't need to continue in the future. However, they both can be used when someone clarifies something that you didn't know, if you reply with 好的, it implies you'll do soemthig based on what you just learned, if you reply with 好了, it means now you already know what's going on, no need of further explaination. 对了 means by the way, it's used for chaging the topic, 好了 can be used to chage the topic, too, but it means you have enough of the old topic, it shows your impatience.

好的means OK. If someone is asking you to do something or telling you a plan. Your answer can be OK / Got it (好的). 好了means you just finished something. 对了mostly means By the way. It has a second meaning: Yes/Correct. But we usually just say 对.

I am not native speaker but will try to explain. Normally 好的 is just same as 好 but 的 helps you to emphasize 好, but 好了 is totally different, it means you just finished something (doing, talking) or gonna finish and gonna switch your talking, doing and etc to new activity, topic etc. Example: - 好了 我结束了 咱们出去走走吧 -好的！走吧 对了 can have two meanings. One is when 了 helps you to emphasize that someone is correct NOW (maybe opposite to what he said lately) . The second meaning of 对了 is close to the english "BY THE WAY" (probably) using before you re telling someone thing that you forgot to tell or supposed to tell before 对了 你还没给我钥匙 ! 对了 你今天不回去吗？