If you mean literally a folder that you have called something like Startup or Start, as your later message suggests, that's not the way to do it.  Having things in a particular folder doesn't load them.  Put them in the Startup Suite in the APPLOAD dialog box [lower right corner; pick on the icon, then the Add button in its sub-dialog box].  It's not a folder but a listing -- the folder locations of such files can be anywhere.

 

The acaddoc.lsp file approach is also good -- include the routines themselves in a file with that name or put (load) functions in it to load them, or (autoload) functions to load their command names but not load the code until those command names are called for [read about (load) and (autoload) in Help].  That file can also be anywhere, as long as its folder location is in the Support File Search Path list, and if AutoCAD finds such a file, it will run what's in it every time a drawing is started or opened.