Learn Italian: Il cane è scappato.

In Italian, the past tense (passato prossimo) uses either avere (to have) or essere (to be) as a helper verb. Verbs that describe movement from one place to another, like scappare (to run away or escape), usually take essere. So, Italians literally say "The dog is run away."

Why does scappato end in -o?

Because this sentence uses essere as the helper verb, the past participle (the action word, scappato) must match the subject in gender and number. Il cane is a masculine singular noun, so the verb takes the masculine singular ending -o.

How would the sentence change if there were two dogs?

If the subject is plural, the past participle ending must change to match. "The dogs" is i cani (masculine plural). The helper verb becomes sono (they are), and the participle takes the masculine plural ending -i, making the sentence: I cani sono scappati.

Does scappato just mean "ran"?

Not quite. The verb scappare specifically means "to run away" or "to escape". If you just want to say the dog ran (for example, to fetch a ball), you would use the verb correre (to run).