>>1016356
Look up "export blender to (game engine)".
There are a lot of skills to learn like uv mapping/unwrapping, texturing, materials/shaders, mesh optimization and triangulation, texture baking for normal maps/ao/etc, and subdivision surface workflows. More important to create and finish things rather than devotedly follow tutorials.

When modeling, you want to aim for a level of detail like the framework mesh in the image. From that, you can create much higher detailed or lower detailed meshes while having the flexibility to change the model. The more you model details into the mesh before the larger shape is finalized, the harder it is to change. For engine export, you'll typically decimate the mesh to lower the face count while still maintaining its shape so it looks like the right meshes more than the left.

You're going to mess up and make models starting with too high and too low of a resolution but you'll learn a lot from redoing your models to work around that.