The notion of the "gay community" is complex and slightly controversial.
The word "gay" is sometimes used as shorthand for "gay, lesbian, and bisexual" and possibly also "transexual" and others, so "gay community" is sometimes a synonym for "LGBT community" or "Queer community". In other cases, the speaker may be referring only to gay men. There are many identifyable "sub-communities" - the leather community, the bear community, the chubby community, the lesbian community, the transgendered community, the drag community, the rave community, and so on.
Some people (including many mainstream American journalists) interpret the phrase "gay community" to mean "the population of gay people".
There are certainly sexual minority cultures which are shared by a substantial fraction of the given minority population. But there are also people in the population who do not share in the culture. Especially in gay villages, the social networks of many LGBT people are heavily concentrated inside the LGBT population. But other people are entirely geographically or social isolated from other LGBT people, or don't feel their social connections to their LGBT friends are different from those they have with straight friends.
Thus it is possible to conceive of a worldwide or a local LGBT culture or social network, but which does not necessarily include all LGBT people in the area. There is also a potential distinction to be made between one's social network and one's sexual network (or universe of possible sexual partners).
Some question the idea notion of sharing a "community" with people one has never actually met (whether in person or remotely). But other advocates insist that all LGBT people (and perhaps their allies), are part of a global community, in one way or another.
The common culture generally celebrates pride, diversity, individuality, and sexuality. Many participants find it a refreshing antidote to hatred, discrimination, sex-negative attitudes, and conformist pressures they sometimes encounter in the larger society.
Political activism is also very common, especially on LGBT, liberal, and libertarian issues (but there are, of course, LGBT people of every political stripe, including Log Cabin Republicans).
Some criticze the "LGBT community" for adopting what they see as negative aspects of larger society, especially commercialism (including treating LGBT people as a distinct market segment or audience), conformism (though it may have different norms to which it pressures members to conform), and ghettoization. Some describe the existence of the community itself as a reaction to societal discrimination. It is arguably a natural outcome for any sexual minority (because of the need to find mating partners), but some have observed that the "gay community" in some very tolerant European countries is less distinctive and less segregated.