'Too' can be used when you want to say that there is more of something than wanted or needed, for example, 'Too much homework' 'So' isn't as extreme, as is often used when you want to emphasise something, for example, 'It was so exciting'. Hope this helped!

very clear exlplaination, I still have much to learn :') thanks John Koekebakker

The difference between the two is how you use them. An example could be "That cat is too big for its age." which would imply that the cat is so big that it is abnormal. If you said "The cat is so big for its age" it would imply the same thing but with less emphasis on how abnormal it is for the cat the be the size it is. It just depends on how its used and where its used! :) Just try to keep an ear out for those words and you'll know when its best to use either or, either way what you say will make sense to a native speaker!