Some uses of the passive voice (verb to be+past participle of the main verb).
We use the “passive voice” when we want to shift the focus from the person or thing performing an action to the action itself or the receiver of the action. For example:

Active: Indigenous groups inhabited the region.
Passive: The region was inhabited by Indigenous groups.

In this case, the emphasis is on the region rather than the indigenous groups.
We also use this structure when the person who performs the action is not known, is not relevant, or we don´t want to mention that person. For example:

Passive: These people were known for their advanced metalwork.

In this case, it is not relevant to know who knew these people for their metalwork, but their advanced metalwork itself.

Now, change the following sentences from the active voice to the passive voice, without mentioning the person who performs the action. Make sure you use the verb to be and a main verb in the past participle.

Example:
Active: They served many delicious dishes at the party.
Passive: Many delicious dishes were served at the party.