Learn French: Ils jouent au football avec un ami. - They play football with a friend.

You don't! In French, the -ent ending for third-person plural verbs (like "they play") is completely silent. You pronounce jouent exactly the same way as the singular form, joue.

Why is there an au before football? Doesn't the English sentence just say "play football"?

In French, you don't just "play a sport", you "play at the sport". The verb jouer is followed by à when talking about sports or games. Because football is a masculine word (le football), the words à and le squeeze together to make au.

When speaking, why does un ami sound like "un nami"?

This is because of a French pronunciation rule called liaison. When a word ends in a consonant (like the n in un) and the very next word starts with a vowel (like the a in ami), that final consonant is pronounced as if it's connected to the next word. This makes the sentence flow more smoothly.

Could I use elles instead of ils for "they"?