3) Negative sentences

To form the negative past form of the auxiliary verbs Be or Can, you just need to add "not" or "n't" to the forms "Was", "were" or "could"

- I was in London ==> I wasn't in London

- We could speak English ==> We couldn't speak English

To form the negative of a sentence of any other verb in the Simple Past you need to use the past form of the auxiliary verb do - that is did + not (often contracted to didn't)+ the infinitive of the verb you want to use, no matter if that verb is regular or irregular:

- Sue arrived yesterday ==> Sue didn't arrive yesterday

- Joe took me to the airport ==> Joe didn't take me to the airport