Linking two shapes

I’m very new to this and I’m trying to link the rectangle I have drawn to the main chassis rail on the right, to form an extension of the chassis. How do I go about this?

image|349x500

Any help would be fantastic. Tia!

image|349x500

@Rhys
Do you want to extend the Rail to meet the Rectangle?
If so it looks as if you could simply Select the end of the rail and pull it to the Rectangle:

If this is not helpful just shout.

I think this would work if they were in line with each other, but the solo rectangle is bellow and to the left of the main shape. Does this make sense.?

It does not look pretty but this is a Tools > Loft from the end of the existing Rail to the Solo Rectangle:

Using a set of Add > Construction Plane then Tools > Loft based on the Rail End may work [MODIFIED]:

There is probably a better way of doing this but more information needed.