Speakers of languages that conjugate verbs for person can and often forgo using pronouns because the subject of the verb is obvious in the conjugation. This is called pro(noun)-drop. There are other situations where pronouns are dropped, even in languages where verbs are not conjugated for person, but pronoun-dropping is normally done when context or conjugation makes it obvious who is doing what to whom, and it would be redunant or clunky to use pronouns.
In Spanish, you don’t need to say “yo hablo” all the time because the verb “hablar” (to speak) is conjugated for first person singular. You would never say “tu hablo,” so it is already obvious who speaks based on the conjugation of the verb. The verb itself is telling you “I speak.”
