Duna and general interplanetary launches mechanics

[Rocket In My Pocket]

39 minutes ago, Actually_New_KSP_Player said:

But i still don't know how to do return mission because many guides (and people here mentioned too) that i don't need such big rocket to do duna's launch because it's overkill, at the same time i wasted almost all my fuel to make an orbit around Kerbin...

When are you going though?

Are you launching using transfer windows? Ie. There is a cheapest time to launch to Duna and a cheapest time to return to Kerbin from Duna.

The difference in Dv cost can be staggering.

[James Kerman]

Congratulations!

This is how I go interplanetary:

1. Leave or return in the transfer window as linked above.

2. Plot and burn a course to your destination.

3. (I think this is where you are having problems) When you are half way to your target perform a course adjustment:
Create a maneuver node 10 or 20 minutes ahead of your vessel - just place it without changing anything.  Then click on your target and select focus view - this will change your view to the destination and should show your plotted course in the sphere of influence of your destination.  Rotate your view until you can see both the path through the SOI and the node you just created and you can now use that node to plan and execute a burn that will bring you close to your intended orbit or even into an atmosphere for aerobraking.  The course adjustment is usually very cheap on Dv and you get savings by doing your capture burn nearer your destination planet/moon (benefiting from the Oberth effect).

4. Profit!

Edited September 16, 2018 by James Kerman
Added info

[Actually_New_KSP_Player]

2 minutes ago, Rocket In My Pocket said:

When are you going though?

Are you launching using transfer windows? Ie. There is a cheapest time to launch to Duna and a cheapest time to return to Kerbin from Duna.

The difference in Dv cost can be staggering.

In main post there's screenshot of planets placement at the start, but i didn't used that mod when i launched since i wasn't aware of that difficult return.. I'll try it on my next launch.