Hey Kimon, how are you?
Well, there are some differences. First of all, "português" is a masculine adjective, so it can refer to things, people, and say that this thing is from Portugal. For example, "Eu tenho um tapete português", so this carpet was made in Portugal. But in addition to that, "português" can also be a noun, referring to a person who was born in Portugal, for example: "O português que mora na casa ao lado é simpático", so the portuguese guy who lives next door is sympathetic.
"Portuguesa" has the same usage, but it is a feminine adjective, so it refers to feminine things, such as "mãe portuguesa" (portuguese mother) and so on.
"Portuguese" is "português" said in English. So you will never find "portuguese" in a sentence. What you will find is "portugueses", which is the plural of "português".
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