JavaScript - dynamic link depending on multiple DropDown Selections or Checkboxes

New to Javascript. Here is the story: I need to create a dynamic link to redirect to one of the 6 different courses, depending on the options chosen by the user. This can be done via 3 dropdown menus or via 3 sets of checkboxes:

img. 1: http://ift.tt/1D0psd1

or

img. 2: http://ift.tt/1Ivs6HD

I tried to combine codes from several examples from stackoverflow, but it's a mess... Any idea is highly appreciated.