it's mostly just spelling to represent different pronunciation of words

nane = none, oot = out, hame = home, mither = mother, doon = down, ye = you, alane = alone, ither yen = other one, dee= die, droon = drown, hairt= heart, ane = one, stane = stone. breid = bread, twal= twelve Those are not so hard really

gaed isnt the same word as "went", I suppose the past tense of go here is "goed". "tirling at the pin" obviously means he knocked at the door (as others wrote, looking at other versions of the ballad would make the meaning plain)
maun = must, winna = won't

I'm sure there are on-line Scots dictionaries
And you could practice reading Rabbie Burns poetry in editions with glossaries, if you are interested.