The files in startup means Windows will pre-load some files for you so when you go to open Skype it will open faster. If you do not pre-load those files (uncheck the box for startup) it won't touch those files during boot, which will make your PC boot faster. When you want to open Skype, it will simply have to load all the files which will take a little longer to start up. Usually uncheck applications that you do not use all the time.
If I boot my computer without some program (for example: Skype) can I still somehow open that program after booting or the program just wont be there?
The files in startup means Windows will pre-load some files for you so when you go to open Skype it will open faster. If you do not pre-load those files (uncheck the box for startup) it won't touch those files during boot, which will make your PC boot faster. When you want to open Skype, it will simply have to load all the files which will take a little longer to start up. Usually uncheck applications that you do not use all the time.
nice video #Ariful4949