Having an array of points(vector2), how do I create a 2d terrain? (new to unity)

You can use http://docs.unity3d.com/ScriptReference/PolygonCollider2D.SetPath.html

Probably a little too late but it could be helpful if someone else comes across the same problem. This is how I solved it. First, make sure each of your shapes (in your case top and bottom) have attached:

• A MeshRenderer with Sprite-Default as material

• A PolygonCollider2D (empty)

• A MeshFilter

Then create a C# script with the code below and attach it to the game object:

 public class Landscape : MonoBehaviour {
 
     private MeshFilter meshFilter;
     private PolygonCollider2D polygonCollider;
 
     void Start() {
         meshFilter = GetComponent<MeshFilter>();
         polygonCollider = GetComponent<PolygonCollider2D>();
 
         // Let's assume you have a FooBar method that returns your array of points
         Vector2[] myArrayOfPoints = FooBar();
 
         // We need to convert those Vector2 into Vector3
         Vector3[] vertices3D = System.Array.ConvertAll<Vector2, Vector3>(vertices2D, v => v);
 
         // Then, we need to calculate the indices of each vertex.
         // For that, you can use the Triangulator class available in:
         // http://wiki.unity3d.com/index.php?title=Triangulator
         Triangulator triangulator = new Triangulator(vertices2D);
         int[] indices = triangulator.Triangulate();
 
         // Now we need to create a color for each vertex. I decided to put them all white but you
         // can adjust it and change it according to your needs
         Color[] colors = Enumerable.Range(0, vertices3D.Length)
             .Select(i => Color.white)
             .ToArray();
 
         // Finally, create a Mesh and set vertices, indices and colors
         Mesh mesh = new Mesh();
         mesh.vertices = vertices3D;
         mesh.triangles = indices;
         mesh.colors = colors;
 
         // Recalculate the shape of the mesh
         mesh.RecalculateNormals();
         mesh.RecalculateBounds();
 
         // And add the mesh to your MeshFilter
         meshFilter.mesh = mesh;
 
         // For the collisions, basically you need to add the vertices to your PolygonCollider2D            
         polygonCollider.points = vertices2D;
     }
 }

I tested it with some random generated mountains and you can see how a box is colliding with these mountains in the screenshot below: