how can i create high quality landscape materials?

Since i started using UE4, i was concerned with the landscape material. I hardly got over tiling textures increasing the maping scale and using lerps. i tought there was no way to get these high quality landscape mats and i became thinking they have been imported from a third party soft or sth. Then i found this tutorial: “Create a Photorealistic World in UE4 - YouTube” by Quixel. he literarly showed the material for 5 s saying sth like “this isn t as complicated as it looks, there are a lot of good tutorials out there…”. Guess what. i found nothing even close to that. I hope you can see some of his comments in the image i attached (best shots i could get to hole material,check attachment). Maybe if u can point me to a tutorial or a right direction, i d be thankful!

So you want us to teach you how to google up Keywords? Pretty much all the comments tell you what to look up.

But to Answer your Question: Experience, Experimentation and Combining your Knowledge of individual Material/Shader techniques into a overall greater Result. So lookup individual Parts, understand what they do and how they Contribute to the whole Result.

The reason this looks good is not the material, but the splat map and heightmap. This terrain is created in world machine which creates realistic height maps with proper erosion, mountai shapes and the like. It calculates where the different textures like grass or rocks are, they are not uniform, more like patches.
His material is very simple, just a rock and a grass texture masked by the splat map

but why you can see tilling at all , the problem with all landscape materials that all of it has tiling and that makes it really bad

Blend in a much larger UV scaled noise pattern to get variation in hue/color/other that makes any tilling near unoticable.

If you never do anything besides assigning a Tilled texture than naturally it will look Bad in the majority of cases. Its not a Problem with Landscapes at all and very easy to solve.