Texture doesn't look the same


I am new to Unity and having problems with the textures. Whenever I import a texture and apply it to the terrain it doesn’t look the same, sometimes it’s for example way too dark and sometimes it’s way too shiny. Here is an example: https://i.gyazo.com/ddcbceb9207f91087aa4f9c46a39e35e.jpg

I have been googling for a while without finding much about it, does someone know what is causing this and how I can fix it?

It’s arguably simply a problem of lightning. Don’t forget that you are in a 3D environment, and that affects your scene. Please check your light sources and modify them.
Otherwise, try using an unlit shader on your object.

Just like beppim suggested, it’s probably the lighting issue. Try to manipulate light on your scene and see if it helps to achieve better result. Also, remember that You can use various mappings to influence the way your textured mesh looks like. Check out occlusion mapping for instance. Whenever You texture a mesh in Unity, You should see a special texture tab (default in the right panel). There You can see what different maps and options You can manipulate to change the way your mesh looks.

Depending on what 3d modelling software You use, You can also generate proper texture maps for Your mesh, that can be applied later in Unity engine.