Do Research

It can be hard to describe sexuality, so do some research if you don't feel comfortable writing. You may want to read stories from other erotica authors to get a feel for the type of description and wording to use. This is especially true for men, who sometimes don't feel the need for description. However, women tend to be more descriptive, so they often have an innate knack for describing things spot-on.

As for the sex scenes themselves, you don't need to have experienced them in real-life, although some authors do choose to go that route. They might describe what they did in first person, which is difficult for new writers.

Also check out... Role Playing: Best-Dressed Ideas 5 Best Places to Have Intercourse Secrets To A Club-Worthy Striptease 6 Ways to Make Your Bedroom Hotter

However it's best to do whatever makes you feel more comfortable. If you do write about a real-life sexual experience, be mindful that it might offend your partner. Be descriptive without making it too publicly known. Try to maintain some anonymity.

Be Uninhibited

Write as if nobody will read it. Let your creative juices flow and just write. It can make you feel vulnerable because you are exposing a part of yourself and your inner fantasies, but you need to be able to eventually be OK with that and gain a sense of comfort. Start out by writing in somewhat risqué language and then move up to juicier scenes once you feel more comfortable.