Tantra could be explained as the Art of becoming a Master of the Sexual Energy. Not by suppressing the energy but by transforming it into the Kundalini Energy. Kundalini is the strong existential energy which can lead to spiritual awakening, inner growth, growing into a higher human level, a higher consciousness, the cosmic consciousness.
To understand completely what the words Tantra and Kundalini mean, and the cosmic awareness growing out of that, it is good to watch the video which is here included. But it would be better to read about it also. There is a very good, small book about Tantra: Tantra Spirituality and Sex, written by Osho.
Concerning Kundalini: Kundalini is the Spiritual Energy which awakens in the body when practicing Tantra, or yoga, or both, or sport, or when meditating, or doing nothing at all, spontaneously, or when having (had) sex. It can be very strong, or subtle. It can bring strange, unknown, confusing, reactions, symptoms. It is important to read about it, on websites like this one.
Watch also the three videos: The Human Body Energy Centers
If you might experience difficulties with Kundalini energies, with unfolding spiritual energies, which are problematic, search for a therapist. You could use the Bach flower remedies also. Search for a Bach flower therapist then.
Header: detail from the Kundalini Guide Homepage