Learn Portuguese (Portugal): Ele deve dormir: está cansado.

The verb dever can mean both "must" and "should" depending on the context. Here, because it is advice or a logical conclusion about him being tired, "should" is the most natural translation in English.

Why is the verb dormir in its full dictionary form?

After the verb dever, the second verb always stays in its infinitive (the dictionary form). This is just like English, where we say "should sleep" and not "should sleeps".

Why do we use está instead of é for "is"?

Portuguese has two main verbs for "to be": ser and estar. We use estar (and its "he" form está) for temporary states or conditions. Since being tired is temporary and will pass after he sleeps, está is the correct choice.

Why isn't there a word for "he" before está?

In Portuguese, you do not always need to repeat the subject pronoun. Since we already established the subject is ele (he) in the first half of the sentence, we can drop it in the second half. The form está makes it clear we are still talking about him.