Flight planning consists of three big theoretical subjects, General Navigation, Radio Navigation and Flight Planning & Monitoring. Its not easy, usually during VFR flight planning you would learn the basics. How to use a map, measuring tracks and distances, use if aircraft performance tables using the flight computer to calculate heading and groundspeed using the forecasted wind, take-off and landing performance, weight and balance.
When I was an instructor we used to let the student do all of this by hand on paper. Once they moved on to IFR they would understand the basics and it would be a waste of time to do everything by hand, so the students were using a excel planning tool (link below) which did the “stupid work”.
The student only has focus on specific IFR planning techniques and type this into the excel which then did the rest. Skyvector is a useful tool to crosscheck the route but its not all that useful in creating the route itself (talking about real world flight planning). Best would be to use a Jeppesen or Navblue IFR en-route chart instead.