If you're asking for formulas that give the distance and direction between two given lat-lons--
There's one set of formulas that gives accuracy to a millimeter, but programming them into your calculator will take a while
There's another much simpler set, about as accurate but only up to 100 km or so
And another even simpler set that gives distance correct to a few meters over lines several thousand km long, but dunno about the directions it gives
Or would you settle for a website that calculates it for you?