Depends how advanced you want to get. Simplest would be to vertex paint your mesh where it intersects with the landscape. You’ll need to understand some basic concepts like material layering and world aligned textures in order to do this.
Next you could use distance fields, but as Al said this is costly.
You could after that try instead importing your terrain height map as a texture , and mapping it inside the material in order to achieve the same effect as distance fields. This is a little bit more intintimidating if you are new to materials.
Finally, you could use decals and place them around each mesh you wish to blend.