How do you build complex structures?

Thankyou everyone for all the help!!! :)

reverse engineer

You can select a part and hold shift + wasd to nudge parts

You could copy my Falcon Heavy and see how I made it. :)

@reCarn Thankyou!!!

There are multiple tools that allow you to rotate/orient objects in any specific way and most objects are procedural meaning you can adjust the shape( up to a certain point) into whatever you want. I suggest playing around with the designer a bit more and take up some of the challenges for a better idea.

Just use many fuselage blocks