That's odd. Are you using the website or the app on a phone or tablet (even in that case it's possible to tap the word to see the translation). Or, (hardly possible, I think), are you taking the "Test Out" option instead of doing the lesson, inadvertently or otherwise? Any other relevant information?
The use of "ol", which is the stem of the verb "olmak" (to become) is described in the notes on the front page of the skill To be - but only in the web version. "Ol" is used as the informal imperative, or command form, of the Turkish non-verb(?) "To be". Similarly, "Olun" is used as the formal version. (Presumably for singular and plural - though I'm not certain of that. And I don't know how you say "Let's be good", i.e. "Let us be good".)
"This same suffix [olun] gets added to all verbs to make formal commands."