When it’s a period that’s finished and done with, it’s am, when it’s still going on it’s ers:
O’n i’n gweithio fan’na am dair blynedd
I worked there for three years
Dw i’n gweithio fan’ma ers tair blynedd
I’ve been working/I’ve worked here for three years
I get it! Diolch!
I also use ar gyfer = for the purpose/preparation of’…but might be wrong?..
Dwi’n gwisgo ar gyfer parti … etc
what are the dialect differences between eisiau/ moyn and angen?
Diolch!
There are probably various ways of answering this, and others will know more than I, but one difference, I think, is that northern speakers don’t usually use “moyn” at all, whereas southern speakers use both moyn and eisiau, but they use eisiau slightly differently to the way northern speakers use it (when it is often spelt “isio”, at least when representing colloquial speech).
What Im aware of is
in the north:
Eisiau = want / angen = need
In south
Eisiau = need / moyn - want
But can eisiau mean want in southern Welsh?
Ideally, in the South -
dw i’n moyn– I want
ma eisiau i fi – I need to
(from the SSiW Challenge 1, Vocab text)
However, as in English, dialects are somewhat interchangeable. So, regarding your question “can eisiau mean want?” - if I was to hear “dw i’n eisiau”, I would personally take it as “I want”.
Edit:
Now I can’t get that Meatloaf song out of my head. 
Revisiting this post as it is something that has struck me recently. What does it sound like to a native speaker of Southern dialect when they hear a Northerner saying Dw i’n isio? (Assuming that they are unused to North Welsh) Is the immediate impression one of someone saying ‘I need’ rather than ‘I want’?
Would it not, now, be recognised due to TV and radio? Just as, in England, local dialects may be becoming more easily understood because of series set in, say, Northumberland and Yorkshire? Before S4C, i doubt if a person from Llanelli would have understood angen and, to them, dwi isio would have been very odd and might well have been thought to mean ‘need’, but hearing Rownd a Rownd…!
I’m really talking about before the media made everyone familiar with other accents (it was the same in Ireland - a couple of native speakers told me that they found Donegal Irish a bit difficult to understand before Irish language radio came along as they would rarely have heard it otherwise). Although even if you know a word means something different you might still find it hard to erase completely the impression of what it means to you in your own dialect.
I did notice, in Tuesday’s Rownd a Rownd (09/05, http://www.s4c.cymru/clic/e_level2.shtml?programme_id=536271496) at 17:46 Jac says to Lowri in the course of that conversation “Ti oedd moyn gwybod”, which surprised me a little, as I hadn’t really come across it before. There’s no reason to think Jac speaks particularly southern, is there?
(Also, while we’re at it, as a newcomer to Rownd a Rownd: why is it that David’s accent sounds very precise but almost English to me? Am I missing either a linguistic implication or a significant bit of backstory?)
Looking for a little bit of enlightenment! In Level 2 challenge 19, I can hear both dy helpu di and helpu ti. My middles tell me to use the one I know and wait and see if a pattern appears, but if anyone knows of a reason why both have appeared, could they share it with me? I’m just going to see if I can find the whole sentence for a bit of context…
Dw i’n fodlon helpu ti Ddydd Mawrth.
Dw i’n fodlon dy helpu di gyda’r trefniadau.
Sorry. It should have been dwi eisiau or dwi isio
I suspect @mikeellwood is better at remembering the plot lines than I am, but, as I recall, Jac comes from South Wales and so does David. I tend to think David’s accent is of a posh boy who has learned Welsh, or a southerner trying to sound posh, but I do not claim to really know!
Just to help you get used to the range of variations you’ll hear in speech - ‘dy helpu di’ is more ‘correct’, but ‘helpu ti’ or ‘helpu chdi’ are very common…
One very small point - they’ll hear ‘dwi isio’ not ‘dwi’n isio’ - the ‘yn’ is dropped with isio. I would imagine that the northern usage is pretty familiar to most speakers by now - and ‘isio/eisiau’ as want is also a very common pattern in teaching, including in the south.
Ye, sorry, the incorrect spelling was my lazy editing from “dw i’n moyn”. I was too slow with my correction, also. 
Thank you. How surprising for me to favour something slightly more correct! Mind you, that’s not likely to develop into a habit so I suppose I shall enjoy it just this once!
At the end of sentences, “isn’t it” or similar is often used, isn’t it? (
) like - on’d ydy? Or d’ydy? Or on’d yw e? i fe? Ayyb
What’s the “won’t it”/“wouldn’t it” version? Would you say a form of fydd?
Also, wasn’t it? On’d oedd?
Thanks in advance
Yup.
Won’t it - ‘oni fydd’, properly, but you’ll often hear just ‘fydd’…
Wouldn’t it - I’d imagine this ought to be ‘oni fyddai’, but I’ve never heard that - only ever heard ‘fyddai’…