Learn Finnish: Lento on peruttu. - The flight is cancelled.

It describes a present state that resulted from a past action. The cancelling happened in the past, which is why we use the passive past participle peruttu (cancelled). But the flight is currently in that state, so we use the present tense on (is).

What is the base verb for peruttu and how is it formed?

The base verb is perua (to cancel). Because it is a verb type 1, we form the passive past participle by taking the strong stem peru- and adding -ttu. This creates an adjective-like word meaning cancelled.

Why is lento in the nominative (basic) form instead of the partitive?

Even though passive sentences often use the partitive for their object, this sentence functions like a basic descriptive sentence (A is B) describing a resultative state. We are describing the current state of a specific, whole flight, so the subject lento stays in the nominative.

Lento means flight. How does it relate to the verb to fly?

The verb for to fly is lentää. By taking the root lent- and changing the ending to -o, Finnish turns the action into the noun lento (flight). This is a very common way to build nouns out of verbs in Finnish.