Our mail box is 1/2 a mile away from our house, so I have to walk down there to get the mail (sometimes there's nothing in the mailbox). Sigh country life. -_-
Sentences in the present tense in Welsh are basically formed as:
[person/thing being + yn + action]
Dw i + yn + canu
"I am" + yn + "sing" = "I sing"
Mae Jac + yn + hoffi
"Jac is" + yn + "like" = "Jack likes"
So the yn connects the "person being" bit to the action bit. It doesn't translate into anything in English really, but without the yn the sentence makes no sense in Welsh.
It's the same pattern in the negative.
Dw i ddim + yn + hoffi
"I am not" + yn + "like" = "I don't like"
Dych chi ddim + yn + cerdded
"You're not" + yn + "walk" = "You don't walk"
i believe it's to connect the sentence. Without 'yn' it would state "I do not like walking", which still makes sense. Just with the 'yn' it completes the statement -ie "I do not like /to/ walk"