The word Completar in Spanish means "to complete." In the context of Lección 3, it is almost always a fill-in-the-blank activity. You will see a paragraph or a series of sentences with missing verbs. Your job is to type the correct conjugation based on the subject (yo, tú, él/ella, nosotros, ellos) and the tense (presente de indicativo).
The subject pronoun is often implied. Look for clues: estructura 31 completar leccion 3 link
In most Spanish textbooks following a standard curriculum, Estructura (Structure) refers to a specific grammar section. Lección 3 typically introduces one of the most important topics: Present tense of irregular verbs (especially ser, ir, dar, ver, oír, and stem-changers) or Possessive adjectives. The word Completar in Spanish means "to complete
Specifically, Estructura 3.1 in many programs focuses on: Knowing this is crucial because the "Completar" exercise
Knowing this is crucial because the "Completar" exercise will ask you to fill in the blanks with the correct form of these exact verbs.