Texture apply

there are a few very good sources on Youtube if you need help with that.
try out Blender guru, he has many different tutorials that go into texturing different types of objects. pick a tutorial with a item that resonates with you, and try it out.
https://www.youtube.com/user/AndrewPPrice/videos

good luck

Grab yourself Substance Painter if you can and forget Blender.

Look into Low-poly retopology and UV coordinates. From other point of view realistic texture may combine many layers (dirt, scratches and so on) - see Substance Painter tutorials on Youtube...

u can go with mari 2 or substance painter for realistic textures