How do I prepare images for A4 magazine Print? My images are 5000px x 4000px at 72 ppi. What steps to do in Image Size Menu Photoshop?

In Photoshop Menu bar, click File/ New and in the pop-up dialog you will see Preset. Under Preset, toggle International Paper, and you will see A4 size ... just click ok. 

In the image you want to print, in the layer of the specific image, just right click and duplicate layer, and choose the previous document which is the A4( untitled 1 if you not named it) the press ok. Resize your image to the A4 paper by transform tool. Good luck! :D