Estaba is the conjugation of the verb estar that matches the first person singular, which is <em>yo, </em>in the imperfect tense. This tense is used when talking about past actions, conditions, or events that occurred regularly or frequently or that were in progress in a moment in the past. Finally, we can write this sentence as follows:
<em>Todos los sábados yo </em><em>estaba</em><em> en la casa de los abuelos</em>
Whose translation is:
<em>I </em><em>was</em><em> in my grandparent's house every Saturday</em>