Learn Swedish: Vi ringde aldrig kunden. - We never called the customer.

The infinitive is ringa (to call). To make the simple past tense (preteritum) for regular Group 2a verbs, you take the stem by dropping the final -a to get ring-, and then add the suffix -de. This gives us ringde.

Why does aldrig come after ringde when we say 'never called' in English?

This is because of the Swedish V2 rule. In a main clause, the verb must be in the second position. The subject Vi takes the first position, so the verb ringde must come next. This pushes sentence adverbs like aldrig to the third position.

Why is the word for customer written as kunden instead of just kund?

Kunden is the definite form, which means 'the customer'. The base noun is en kund (a customer). Since it is an en-word, we attach the -en suffix to the end to make it definite.

Do I need to use the preposition till (to) when saying who I called?

It is completely optional! You can say Vi ringde kunden or Vi ringde till kunden. Both versions are common, correct, and mean the exact same thing.