Could you explain why ‘Eu estou’ versus ‘Estou’, are used. I think are the same thing but cannot work when to use which, or are they interchangeable?
Thank you.
@minns01, they are interchangeable 
In Portuguese, we can often omit pronouns because we can infer the grammatical person from the verb conjugation and from context. But explicitly adding the pronoun is also perfectly fine to do and actually advisable whenever the focus changes from one person to another, for example. So you’ll often see us mixing it up in conversation.