Problem regarding rectangle shape

I have tried both methods suggested by Byron and Towerguy. I'm still unable to get done what I want to do. I don't know if I'm not following your instructions right guys, or if I'm just dumb. 

I have already clicked (turned off) both the Transform: Rectangle 1 and Transform- chain icon scale settings but still I get no result.

Neither the anchor point or the Bezier Path did anything either. I guess I'm not explaining myself right.

I just want to move it as if it was in Illustrator: you click on the right-middle point, you drag it to the center and then you can get half a rectangle.

I guess is sort of wanting the three points -on one side- to move simultaneaously somehow, not the whole rectangle or a specific point. Do I have to select the three points, or is it the way I have set up the project?

Hi. Move your anchor point to the left edge of your shape (it's the cross hair shape in the centre). There is a tool at the top called the Pan Behind Tool which does it (shortcut Y). Put the cursor over the anchor point, left click and drag to the left edge. Look up tutorials on changing the anchor point as it is a very useful (and basic) thing to know and understand.

Proportional scaling is accessed in the layers dropdown Scale setting - click on the little chain icon to turn it on or off.

If you already have the shape created, right click on the content of the Shape Layer / Convert To Bezier Path, then select the Convert Vertex Tool and you know the rest.

Try this:

Create the shape while holding down the Alt key.

Then choose the Convert Vertex Tool.

Now move the point you need by holding down the Cmd key on Mac or Ctrl on Windows.