DRAWS EXPALINED ???

I would like to ask the members on WW. about an issue that has troubled me somewhat ,and that is ,these competitions ,draws etc latest one is for The Rugby Union W.C.Final ie prize money a few days in Paris etc , then there is one doing the rounds called "OMAZE " FOR A TICKET COULD NET YOU A property £100k in cash , So to my question when these comps are advertised it tells how how to apply ,by text ,phone .mail .etc NOW this is what i want to know with all these differant choices to try and win ,
"JUST HOW DO THEY ARRIVE AT A WINNER ???????
G.B.