We get dangerously close to a semantic difference here, but this is how I learned the categories generally work. This is not my field, so I could be wrong, of course.

Generally, you can break things down to three categories.

There are reflexes, which are when your body reacts to something without your brain needing to be involved. The latching reflex in babies, for example, or the patellar reflex (tapping the knee to make the leg jerk).

Then there are instincts. Instincts involve the brain, and so generally don't appear in human infants immediately. Instincts are like pre-written scripts encoded in us, but require a level of development before those scripts can be executed.

Then there are learned behaviors. Things that are "intuitive" fall into this category. Something is intuitive if a behavior you already know well can be applied the activity.

Reproduction is instinctive (and it's an instinct that, in humans, doesn't really show up until much closer to sexual maturity). It's not intuitive. If you've never been exposed to or taught how to have sex, you'll still feel the desire and be able to do it. Maybe not well, but you can get the job done.