You don’t necessarily need an account on lemmynsfw.com - you would just need an account to browse NSFW on their homepage. But you can see and interact with all their communities from your current instance.
Just search for the communities while on lemmy.world - for example !porn or !boobs or whatever. You can click on those.
Just make sure you have “Show NSFW” enabled on your profile settings
Now some instances like lemmy.ml decided to block (defederate) from lemmynsfw.com so YMMV