Next to fly, you will need power, the technical term is called the "Thrust". The thrust can either pull the plane foreward with a puller propeller, an EDF (ELECTRICAL DUCTED FAN) ETC.
Now you will need the fuselage, fuselages can vary from different types of aircrafts. Most planes have a 3d scale replica of a real airplane; Some can have a completely scratch buil models sanded off with fan fold insulation foam, but the most exciting type of fuselage is he complete flat profile models, they can perform 3d aerobatics and more.
Step 1: Wings
Some wings are cut out from balsa wood, those are usually the scale models. But some wood can be heavy.