Custom Brushes

Create a new document any size, create a new layer and draw an object, color the object black.

Control click on your layer to select your object.

Goto "edit > copy" OR "ctrl + c", then goto "file > new", leave all the settings apart from the background settings, change this to "transparent".

Now once the new document has been created goto "edit > paste" or "ctrl + v".

Press "ctrl + a" to select all and goto "edit > define brush preset" label your new brush.

Now create a new document with your desired background color. Select the paint brush tool then click the menu at the top (see image below).

Select your brush and away you go.