So is used to show agreement with positive statements. When we use it, it is the same as using too. For example, Marline smokes pot. If you also smoke pot, then you could say a few things, including So do I, or I smoke pot, too, or Me too. They go from least colloquial to most colloquial. The word order is so + auxiliary verb + noun/pronoun/name/etc. Check out the examples in the table below.

As you saw, in our formula above, it is possible to replace auxiliary and the pronoun [So did John], depending on what the original sentence that we agree with is. Remember... we use so only in agreement with a positive statement, and not to disagree with them. When we disagree with positive statement we still need the original auxiliary/modal verb. In our example above, if you don't smoke pot, you'd say I don't or Billy doesn't or My parents don't.

Nor is used to show agreement with negative statements. When we use it, it's like using too. For example, Marline doesn't smoke pot. If you also do not smoke pot, then you could say a few things, including Nor do I, or I don't smoke pot, either, or Me neither. Like for agreeing with a positive statement, they go from least colloquial to most colloquial. The word order is Nor + auxiliary verb + noun/pronoun/name/etc. The word nor is similar to the word neither. You should pick the one you prefer and stick with it. Nor should they is exactly like Neither should they. Again, have a look at the examples in the table below.