One thing I always forget the rule to in Portuguese is the difference between abaixo and a baixo. The both sound the same, and they both essentially mean the same (or do they?!). And because of this, I always find myself asking my coworkers time and again, “Ok, I know I’ve asked you this before, but… for this sentence, do I use abaixo or a baixo?”
And so I finally decided to look it up myself to see if it would stick! It’s really, quite simple. Hope this helps you all as well 
Abaixo – with all the letters together, abaixo means under or below. It speaks to something that is positioned in an inferior position to something else. It is an adverb.
Examples -
Segue as minhas respostas abaixo. = My responses are below.
A padaria fica logo abaixo do meu apartamento = The bakery is right under my apartment.
Fun Fact: Abaixo Assinado is the term for “Petition,” and means, “Signed below,” which is what a petition is, no?
A baixo – Separated after the “a,” is always used with a “from above” type reference. It means, essentially, down or bottom. It is an adverbial phrase.
Examples -
Eu li aquela carta de cima a baixo e não encontrei nada = I read that letter from top to bottom and didn’t find anything.
Ele me olhou de cima a baixo, fiquei muito contrangida = He looked me up and down, I felt very awkward.
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Entendeu?
