CastStartPosVec - Point where you start cast from. Usually equals to your position. To get: GetOrigin(GetMyHero())
EnemyChampionPtr - Pointer to enemy champion. Usually equals to your desired target.
EnemyMoveSpeed - Move speed of enemy champion you chose as target. Usually equals: GetMoveSpeed(your_target_pointer_there)
YourSkillshotSpeed - Speed of your skillshot. If you are physicist, you can calculate time and distance and find a speed. Else, use various SpellDataBases or use RiotDecoder.
SkillShotDelay - Delay, before your hero casts a spell itself. Usually it is nessesary to look in SpellDataBases. But you can use value '250' (milliseconds) most of the times. Be careful, for example, Cho'Gath have value of 3000 (or around so)
SkillShotRange - Range of your skillshot. Usually equals to range of your skill that you used. To get: GetCastRange(GetMyHero(), usedSpell), where usedSpell is _Q, _W, _E or _R
SkillShotWidth - Width of your skillshot. Can be found in SpellDataBases or RiotDecoder
MinionCollisionCheck - set this to true, if skillshot will stop after hitting a minion. Else (if it can go through it) - set to false.
AddHitBox - I don't know what it is, just set is as 'true'.