There have been alot of new users that migrated from youtube and don't know how to make their creations fly. Here is a tutorial on how to build your plane.

Propulsion: you want to have a fair amount of propulsion that suits your plane well. smaller planes would normally go for props and even the blasto J15. medium sized planes need the J50 and the J90. the large planes need the BFE120 9r a modded vtol engine. If you place these engines internally, you need an inlet on the outer fuselage.

Flight Balance: in order to fly properly, you need the correct order in wheight and lift. The further the CoM (red) is from the CoL (blue), the more stable. Try to keep the close but still distant from each other. If you want to make it nimble and agile, you want to make the CoM and CoL close as possible and make the control surface as short in length as possible. You also need the back gear to be behind the CoM.

Speed, Controls, and Looks: If you want speed, you need a sleek outside. A way of doing this, is using the fuselage block and nose cone. If you highlight these parts, you can edit the width, height, and length of them. They also give you the option to dead weight, fuel, ans bouyancy (float on water). with these tools you can do a lot with making planes.