Learn French: Ils perdent souvent notre colis. - They often lose our package.

Perdent is the ils (they) form of the regular -re verb perdre (to lose). To form it, you drop the -re and add -ent. Just like with regular -er verbs, this -ent ending is completely silent. You pronounce it exactly the same as the singular form, perd.

Why is souvent placed after the verb instead of before it?

In English, we usually put the adverb before the verb (they often lose). However, in French, short adverbs like souvent (often) are placed immediately after the conjugated verb. This gives us ils perdent souvent.

Since colis ends in an 's', does that mean it is plural here?

No, colis (package) is a noun that naturally ends in an 's' even in its singular form. You can tell it means exactly one package here because it uses notre, which means 'our' for a singular noun. If it were multiple packages, it would be nos colis.