Beginners are rarely rude on purpose. They sound abrupt because the polite version of a sentence is longer and harder, so they say the short one — and the short one, in most languages, is the command.
Directness is the default when you are limited
“Give me water” is easier to build than “could I have some water, please”. So that is what comes out, and it lands far harder than you intended. This is the single most common reason learners are perceived as impolite, and it has nothing to do with attitude.
Learn the softeners before the vocabulary
Every language has a handful of words that turn a demand into a request: the equivalents of please, sorry, excuse me, would, could, maybe, a little. They are short and they do enormous work. Learn the polite frame once — could I / would it be possible / I would like — and then drop any noun into it. One structure covers a hundred situations.
Politeness is not distributed the way you expect
Some languages put it in verb endings, some in a formal pronoun, some in how indirect you are, some barely use please at all and would find your version of it stiff. Copy what people around you do rather than translating your own habits. Over-formality is its own kind of mistake, and it is harder to notice.
When in doubt, add a reason
Across languages, a request with a reason attached reads as far more polite than the same request alone. Sorry, I am late, could you help me — the reason does most of the softening. It is also easy to say badly. A clumsy reason still works; a missing one does not.
You do not need advanced grammar to sound courteous. Six softeners and one polite frame, used early, will make your limited language read as warm rather than brusque.