Final answer:
To conjugate -ar verbs in the present progressive tense in Spanish, you add -ando to the stem of the verb.
Step-by-step explanation:
In Spanish, to conjugate -ar verbs in the present progressive tense, you add -ando to the stem of the verb.
For example, let's take the verb 'hablar' (to speak). The stem of the verb is 'habl'. To form the present progressive tense, you add -ando to the stem, resulting in 'hablando' (speaking).
So, to conjugate -ar verbs in the present progressive tense, you add -ando to the stem of the verb.