Surrogacy in where a woman carries a child to term on behalf of other people with the intention of giving the child up when s/he is born. The surrogate mother is usually the genetic mother of the child.
Surrogacy arrangements involving lesbians and gay men are still extremely rare in the UK. Elsewhere it is possible to enter into commercial surrogacy arrangements, but legally this is problematic and legal advice should be sought if you are seriously considering this option.
It is also possible to enter into an arrangement where the intended carers of the child have no biological relationship to the child, again specific legal advice should be sought if this is being contemplated.
The legal "parents" in this type of arrangement are the surrogate mother and the donor. The donor would not have any automatic rights in this situation but could apply to the courts as an unmarried father.