put one image on top of other in photoshop cc 2017

You can drag one image on top of another (from one tab to the other) using the Move tool. You can check the images in the Layers panel.

(Your image link above isn't working – use the facility at the top of this panel as indicated in the screen shot below.)

There are multiple possibilities to achieve this. I will give you one.

The initial state is this:

Double click the "Background" layer to convert into a standard layer. Background layers do not have transparency. The name of the layer is at your discretion.

I've added now a black "Colour Fill" layer and used the magic wand to select the white colour.

Select->Inverse to invert the selection. You can now add a layer mask to the layer.

(look at the blue line for the colour fill, red line for the mask). The mask is a b/w image, white is opaque, black is transparent, any shade of grey is more or less transparent. Layers can be rearranged by dragging the layer up or down. It is irrelevant here, which operation you do first: Select->Mask or "colour fill" layer.

The selection imperfections result from the anti-aliasing used in the original picture.