"If someone is unaccustomed to it, there does need to be a bit of gentle technique. It's not really my thing too much but I've done it a few times just for the experience.
A bit like with newbies to anal, start very slowly and gentle and there is no such thing as too much lube. Go in little stages initially, so if two finger is too tight (which I doubt, because my dick is bigger than two fingers, but whatevs) then just get her or him used to it first. Take your time, then when someone is used to that, increase.
Eventually you'll get to the point where four cramped fingers can get inside, at that point start to curl your fingers internally etc. It should be obvious from there, there must be stuff about this online so Google the hell out of it and just remember to go slow.
So long as everyone is having fun, that's all that matters, don't let sex be some weird competition."