all recipes on this site are vegan unless otherwise specified, because i, the writer, happen to be vegan (mostly. with nuance). however, many of my own recipes i have adapted from non-vegan sources; most of the time i just do straight 1:1 for butter to oil, dairy milk to non-dairy milk, etc and that works fine. other, more specific conversions are listed here.
generally, when substituting ingredients you want to keep the same volume of material, otherwise you'll have to increase or decrease the other ingredients in proportion. keep this in mind especially when substituing liquid for solid ingredients and vice versa so you keep your measurements accurate.
the suggestions on this page are just that: suggestions. they might not be universally applicable to all recipes, so keep your own tastes in mind, espcially because you are (probably) the one eating it anyway and you can make things however pleases you. there are no "right" answers to food.