“Either” and “neither” are used in negative sentence to show agreement.(NEITHER = NOT EITHER)
Structure :
1. NEGATIVE SENTENCE, EITHER.
2. NEITHER + AUXILIARY + SUBJECT
Auxiliary (do/ does/ have/ should/…)

Example 1 :
Person A : I don’t love football.
Person B : I don’t (love football), either.
Person C : Neither do I.

Example 2 :
Person A : Shaym can’t swim.
Person B : I can’t (swim), neither.
Person C : Neither can I.