In English, questions beginning "Can you...?" can be used either to inquire if someone is able to do something ("Can you swim?") or to request someone to do something ("Can you shut the door, please?") Do questions beginning "Wyt ti'n gallu...?" in Welsh work the same way?
If you want some to do something, but you do not want to 'order' them to do it you can use wnei di...?, wnewch chi...? (from the verb-noun gwneud):
- Wnei di agor y drws, plîs? Gwna, wrth gwrs - Will you (= can you) open the door, please? Yes, of course.
- Wnewch chi rywbeth i mi? - WiIl you do something for me?
- Wnewch chi ymddiheuro drosto i? - WiIl you apologise on my behalf?
Nowadays medru and gallu as verb-nouns both mean the same thing. The usage does vary between the 4-5 main dialects, but both should be understood all over Wales.
(gallu and medr (no -u) also exist as nouns meaning 'ability', 'skill', etc.)