"Sioned dw i."
Translation:I am Sioned.
I didn't know the answer before I tried to answer your question, but: as a general rule, it's a "sh" when you have "si" followed by a vowel sound, in words such as "siwgr", "esiampl" or "siawns" and it's an "s" when there is no "i" or when that's followed by a consonant, in words such as "sicr", "sidan" and "sinamon". In a casual look through, I couldn't find any that weren't loan words from English, though (even "sicr" is from Middle English "siker"), which is interesting.
There are two basic ways of constructing a sentence in Welsh.
The first is the normal Verb-Subject-Object
eg 'Ces i siocled' = I had chocolate (lit:- Had I chocolate)
In the present tense we use 'Bod' the verb 'to be'
eg' Dw i'n hapus = I am happy (lit 'Am I happy') or your example 'Dw i wedi blino' = I am tired (lit 'Am I tired)
The second way of forming a sentence is the emphatic one where we change the word order.
We could use it in your example:- 'WEDI BLINO dw i' = 'I am TIRED' (Lit:- TIRED I am)
However that useage is a bit archaic, these days it's only really used to express names and jobs.
Sioned dw i = I am Sioned :- this is very common in Welsh as a way of introducing oneself
Meddyg dw i = I am a doctor :- this is the standard way of talking about a job