"I think that the dress is very expensive."
Translation:Yo creo que el vestido es muy caro.
No it's not necessary at all. You can almost always omit personal pronouns in Spanish. With time you'll figure out when to say them or not. Basically it depends on the emphasis you make in a sentence. It's just a matter of "how it sounds". Something that you acquire with time and practice.
No sé por que este me está diciendo que "pensar" no es correcto Yo siempre estoy hablando con mis amigos quienes hablan muy bien el español. Pero ellos me dijen que es súper perfecto. Pero, ¿Por qué?, ¿Por qué este me dije que es no correcto?
I do not know why it is saying that "Pensar" which I said it is wrong. All of my friends who speaking Spanish told me that I can say whatever I want "Pensar or Creer" But they said if I am talking about something that I believe I'll be saying "Creer". So, Why can I not say "Pienso" instead of "Creo"?. I believe that it is expensive and I think of it is expensive at the same time. lol... Did I something wrong with that??
"Pienso" works as well. It should be fixed. Maybe it's more common to say "creo" in this case, but "pienso" works all the same.