How does the whole dress shopping process work?

I am starting to get quite stressed about dress shopping! How does it all work? Some places say they like 9-12 months to make your dress but I am assuming that doesn't include alterations? I am getting married in Oct 26 and have some appts booked for the end of Nov. Just for a rough idea- whats the process? I go and try on dresses, find the one I love, order it, wait for it, then take it to be altered? I am hoping to lose some more weight and tone up before the wedding (I have a whole year pretty much) but how will that work with alterations? Are they usually done closer to the wedding or as soon as I get the dress? Can someone pretty please outline the process for one clueless bride? Yours sincerely, a very stressed gal xx