Order of creation of instances

I have the following classes:

class X
{
    int x = 100;
}

class Y:X
{
    int y = 100;
}

and the following decompiled code:

class X
{
    int32 x;

    public void X()
    {
       this.x = 100;
       base.Object();
    }
}

class Y:X
{
    int32 y;

    public void Y()
    {
       this.y = 100;
       base.X();
    } 
}

so when I create an instance of Y as in new Y(); I thought that first is created an instance of X type and then an instance of type Y because X is the base class and that base class must be created first than its derived class (Y).

However reading the decompiled code this exists before base and how is possible if base should be created before than this?

Maybe does it exist only one object? And we must always call, first, base class constructor only for initializing purpose?

Practically which is the raison to call first base class constructor if we cannot must create first an instance of that type?

Very confused!