Polite requests with 'queria', 'gostaria' and 'podia'
When Portuguese speakers ask for something politely, they often avoid the plain present tense. Instead of quero (I want) or pode (can you), they shift the verb into the imperfect or the conditional: queria, gostaria, podia, poderia. The request stays the same, but the tone becomes softer, a little more distant, and more courteous.
English speakers know the idea, since English also says I would like and could you. What trips them up is the imperfect. Queria looks like it means I wanted, a past tense, so it feels strange to use it in a café right now. In Portuguese, though, this imperfect is one of the most natural ways to ask for something.
Take a verb you would use to make a request and move it one step away from the present. You can use the imperfect (queria, podia, gostava) or the conditional (gostaria, poderia). Both soften the request. The imperfect sounds warm and everyday. The conditional sounds slightly more formal and is especially common in Brazil and in written Portuguese.
The present tense is not rude in itself. A plain Quero um café with a friendly por favor is normal in many Brazilian cafés. But in shops, restaurants, offices and with strangers, the softened forms are the safe default, particularly in Portugal. Think of it as a volume knob rather than a strict rule: the further you move from the present, the gentler you sound.
querer becomes queria in polite requests. It is the everyday way to order or ask for something, and it works in both Portugal and Brazil. The conditional quereria exists, but it sounds stiff, so stick with queria.
gostar gives gostaria de (conditional) or gostava de (imperfect, very common in Portugal). Both translate as I would like, and both keep the preposition de.
poder turns pode...? (can you...?) into podia...? or poderia...?, the equivalent of could you...? Portugal leans toward podia, while Brazil often prefers poderia.
dever follows the same logic for advice and suggestions. Deves (you must) sounds firm, while devias or deveria means you should or you ought to, which is much gentler.
The most common mistake is dropping de after gostaria. Say gostaria de um café, never gostaria um café. Queria takes no preposition: queria um café.
Asking for permission is different. Posso...? (may I...?) in the present is already polite and perfectly normal, so you do not need to soften it.
Finally, remember that Brazilian service talk is often more direct. You will hear things like the following, and nobody takes offense:
As a learner, though, the softened forms never sound wrong, so they are the better habit.
To sound polite when asking for something, move the verb away from the present: queria instead of quero, gostaria de or gostava de for I would like, podia or poderia for could you, and devias or deveria for gentle advice. The present is not rude, but the softened forms are always a safe choice.