It's actually not that hard, just get into an equatorial orbit around Kerbin, look for a planet you want to go to, fiddle around with manoever nodes for an hour and turn your engines on in the proper direction. Phase angles are easier though, but take longer. It's like waiting for the other planet to be in the right spot, which takes ages.
idek what these manuever whatnots are, i just do basically the orbiting tutorial over and over (reach lower point in orbit, raise highest point to other orbit).
how would i build something to take me to another planet? everything i've built to reach Duna is unstable as forget and falls over easily.