1. In the GameObjects tab select 3D and select Terrain.

2. Keep the Terrain selected from the Hierarchy and on the inspector select brush tool and from the popup select  Raise or Lower Terrain.

Then use the brush on the selected terrain by clicking to raise and Shift+ left click to lower the terrain.

3. Then on the same brush tool choose Paint Texture. Make sure you have downloaded / your own terrain texture assets and it has been imported to your project. In terrain layers, go to Edit Terrain Layers and choose Create  Layer. Then add a base texture for your terrain. Here i chose Snow.

4. In Edit Terrain Layers , choose Add Layer and select the layer you want from the pop up and then paint it over the region you want.

by Student of VIT Bhopal(CSE with specialization in Gaming technology)