Learn French: J'avais expliqué la confusion au client. - I had explained the confusion to the client.

J'avais is the imperfect (imparfait) tense of avoir. When combined with the past participle expliqué, it creates the Plus-que-parfait (pluperfect) tense. This gives us "I had explained" rather than the Passé composé "I have explained" or "I explained" (j'ai expliqué).

Why does it say au client instead of à le client?

In French, you explain something to someone, which requires the preposition à (expliquer quelque chose à quelqu'un). When à is followed by the masculine word le, they must merge into au. If the client were female, it would be à la cliente, which does not contract.

Since la confusion is feminine, shouldn't expliqué have an extra 'e' at the end?

Not in this sentence. Because this tense uses the helping verb avoir, the past participle (expliqué) only changes to agree with the direct object if that object comes before the verb. Since la confusion comes after the verb, expliqué stays in its default form.

How would I change this sentence to say "I had explained it to the client"?