Please tell me what is the law regarding same sex relations in Judaism?

The law differs for men and women.

Maimonides writes (Laws of Forbidden Sexual Relations, ch. 21) that based on the passage in Leviticus 18:3 - "Do not perform the actions that they did in Egypt where you dwelled," it is forbidden for women to be "misololos" with each other. 

Rashi (in the Talmud Yevamot 76) defines this word as two women lying together the way man and woman lie together for sexual stimulation.

One of the best-known Biblical verses is Leviticus 18:22 which states that male homosexuality is incorrect behavior.

The Bais HaLevi explains: G-d purposely created us with different inclinations for good and bad, and commands us to overcome the bad inclinations by adhering to the Torah. We are all here to perfect a different part of the Torah, according to our unique desires, upbringing and environment.

It is axiomatic that Judaism legislates only acts, not orientations. A desire for lobster dinner is not a violation of Kashrut laws, only the dinner is. The same is true with homosexuality.

The Torah understanding is that people can control their behavior if they're motivated. There may be a predisposition toward homosexuality for some, but there exist many such predispositions. The Talmud says certain people have more of a genetic tendency toward bloodshed. The Talmud advises them to become butchers or Mohel's, to channel their tendency into a useful pursuit.

Imagine a "kleptomaniac" who could only find fulfillment by stealing from other people. How would society respond? Although we'd be sympathetic and concerned for the individual, we still would not be able to tolerate behavior that's destructive to society. This behavior is wrong and, with effort controllable.

There are some people who were born with a greater tendency to be homosexual. It covers a wide range - some more of a tendency, some less. Everyone can overcome their tendency. But once you sanction the behavior as normal, then many borderline people will cross over into that world. Imagine a teenage boy who has had a few frustrating experiences with girls. He may now be susceptible to forging an intimate relationship with a warm and caring man. Many, in our dysfunctional society, are simply blocked in expressing normal love relationships with the opposite sex. That just means that they are chosen to perfect that part of the Torah, by overcoming their inclinations.

For each of us in our own areas, the test is harder, but we all need to overcome our body drives. 

There is much more to be said on this topic, as far as how a homosexual can lead a completely fulfilling life, both socially and spiritually, but you can write back if you'd like to discuss more.