Flash classes...quick?

as i learn as3, and googling up and youtube-ing whatever i can find, i notice that,
in alot of the files i check out for study, i notice that the person teaching will be like

" download this package from xyz.com "

and usually these classes / packages are named after the site or person etc…

does this mean that if i learn this persons tutorial for whatever effect im wanting to learn/implement…that that effect is based on THEIR files only???and do these files dial home?

so for example, everything i need to learn, is it contained in their files alone (completely offline) or is it based on math thats dialing to somewhere on their servers? cause someone told me something crazy like that and i dont want to use something that depends on code that exists/works only when in contact with their server.

sounds crazy i know but…yeah:tini: