A long standing mantra of brewing was to ferment in the plastic bucket for 7 days. Then the beer would be siphoned out of the bucket and into the carboy. In the carboy it would sit for 14 days. This step was used 1) to help with beer clarity as more stuff would settle out here post the primary ferment (done in the pail) 2) to get the beer of the sludge of yeast that will be sitting at the bottom of the pail after 7 days.
Current more conventional thinking has won out that you only really need to do your ferment for most beers for 14 days in one vessle. As a new brewer the buckets tend to be easier to clean and maintain at first, but a glass carboy lets you see the beer fermenting in side and is sort of cool.
I would recommend choosing the bucket and fermenting for 14 days. At the end of the 14 days, check the gravity to be sure you are done. (that may require a couple checks on consecutive days). Go ahead an bottle as directed after that. Then you can get into trying more tricks of the trade with the carboy and a two stage process. But first you should focus on just making a good beer that will encourage you to move forward and do something new.
First time around keep it simple and as worry free as possible.