Nearly all of this movie's scenes include some sort of nudity, and all of those that do progress to sex sooner or later; there is no innocent or casual nudity in this movie. No external part of the human body is hidden in these scenes except by pubic hair typical of this movie's 1971 release.
Some of the sex scenes start with the couple already nude, but most show explicit disrobing.
The genitalia of male participants in these sex scenes are usually shown, though not always, and we usually see the penis erect at some point during each scene.
The genitalia of female participants are hidden only by pubic hair, so that for any given woman, her labia may be anywhere from fully covered to clearly visible through the hair. In one scene, a woman's labia are parted sufficiently to display her vaginal vestibule. (Colloquially, "pink.")
The sex scenes in the movie are a mix of heterosexual and lesbian. In their essence, these scenes are all couples sex, but there is a brief F-M-F grouping. (This quickly becomes F-F.)
In two scenes, a couple showers together, M-F in the first case, F-F in the second. In both cases, full nudity is shown, and the participants progress from soaping each other up to sexual activity.
Copulation is only implied in each hetero-sex scene; all such scenes depict simulated intercourse. No ejaculation is shown.
Most of the oral sex scenes are simulated, but there are a few scenes depicting explicit cunnilingus and one of explicit fellatio.
A woman pleasures herself with a hairbrush. No contact or penetration is explicitly shown, and indeed, the posing and positioning make it doubtful that actual contact occurred on-set.
In several cases, the simulated sex scenes involve goofs in posing or camera work in which a knowledgeable eye sees something biologically impossible, such as body parts that need to touch to achieve congress clearly being many inches apart. Actors are frequently shown responding to touches they clearly cannot be feeling.
Explicit tongue kissing, breast-groping, nipple-licking, nipple-sucking, hand jobs, cunnilingus, fellatio and vaginal fingering are shown in this movie. Of the latter, labial rubbing is clear in several scenes, and explicit digital penetration appears to occur in some of them. In at least one case, the penetration is simulated by the giving actor folding a finger so that only the knuckle pushes in among the labia, not the actual finger.