A game engine is software used to make games. A good game engine like Unity can make the process easy for you.
INKSCAPE
There are a lot of drawing tools available but Inkscape is the best free drawing tool. Even a non-artist can master Inkscape in a matter of days.
GIMP
Gimp is almost as powerful as Photoshop and it’s Free. The main advantage of using Gimp is most of the plugins available in Photoshop are also available in Gimp
Blender
Blender is an open-source software for creating 3D models, animation, visual effects and motion graphics.
Canva
Canva Gives you ready made templates for marketing images for your game. Get professional looking images in seconds