How do I get the mirror corners to get attached at the center, I turned on clipping and they are still not getting attached and move together from the center, What am I missing or doing wrong ? thanks in advance
I'm not sure if I understand you correctly, but the Clipping in the Mirror Modifier works like this:
In your example, imagine an invisible wall where the X-axis is. now move everything in the Y direction as soon as a vertex hits the wall, it can't move further. But it still can move back, so it's not merged with (attached to) its mirror vertex. In order to 'attach it, you need to move it towards the center until it hits the wall (can't move any further) and then release the mouse! Then it will be merged and can't move in the Y direction any more.
A bit of a clumsy explanation, but I hope it helps;)
It worked, Whenever I mirror I have to move it to the center with clipping turned on and it will just attach itself ?
You'll have to move it to the mirroring point. In this case (and very often) that is the World Origin. So, yes, move the point(s) to the center. You can select all points that you want to 'attach' and (with the Cursor at (0, 0, 0) and the Pivot Point set to the 3D Cursor) press S, Y, 0. Then the Y-values of those points will be 0, meaning they all lie on the X-axis. Sounds a bit complicated in writing, but it's something I use 'all the time' when working with a Mirror Modifier.