Espresso Machine coffee amount
The EC-155 comes with two coffee filters and a measuring spoon; the smaller filter one is for one shot of espresso and the second filter is for two shots (see user manual at, e.g., here). 

Fill the smaller (or larger) filter with one (or two) loosely filled spoons and press lightly using the disc that is attached to the machine. 

A single shot is considered to be about 30 mL (1 US fluid ounce) but this is really a matter of taste and personal preferences. For a single shot in a standard size espresso cup, I would suggest starting with filling half a cup and then adjusting the amount of coffee that you pour to accommodate your taste (and need for caffeine...).