Is a facial oil the same as a moisturiser?
Not quite. An oil contains no water, so it seals moisture in rather than adding it. Apply it to slightly damp skin.
How much should I use?
Two or three drops for the whole face, pressed in rather than rubbed. More than that is why skin feels greasy.
Does it go on before or after a cream?
After. Oil is the heaviest step and nothing penetrates it afterwards.
Which size should I buy?
The 25ml lasts a long time at two or three drops a day, so it is the sensible starting point.