i have photoshop and have fooled arround with it for a while but i cant figure out how to get things to go invisible

for instance if u have a picture of a rim but you want to be able to lay it on a new background but want the new background to show between the spokes instead of the old background
or another example you have a picture of a car from a side view and you want to put it in a new background but want the new background to show through the window

i know you can do it it just puts that checkered pattern where you want the lower layer to show through but i dont know how you get that checkered pattern their any help would be appriciated

 

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LoL you mean tutorials right.. titoriuls might get him ****..