LGBTQIA+ (or LGBT) is an English abbreviation for various gender identities and sexual identities– these identities are self-definitions, i.e. they are not determined by the outside world.
In Germany, the German abbreviation, LSBTTIQ ("lesbisch, schwul, bisexuell, transgender, transsexuell, intersexuell, queer") is often used.
Lesbians are women or people who identify as feminine in any way who are attracted to women or people who identify as feminine in any way. Gays are men or people who identify as masculine in any way, who are attracted to men or people who identify as masculine in any way.
People whose gender identity does not correspond to the gender they were assigned at birth are referred to as trans*/transgender/transident.
Inter*/intersex people are people with physical gender characteristics that cannot be clearly categorised as exclusively "male" or "female".
Asexual people have little to no interest in sexual acts.
Being non-binary means feeling neither exclusively male nor female but beyond traditional gender categorisations. This can have different effects; the person may identify as agender (no gender), bigender (simultaneously "male" and "female"), gender-fluid (gender identity is always changing) or genderqueer (has nothing to do with "masculinity" or "femininity").
The plus in LGBTQIA+ affirms that there are other sexual and gender identities.
Queer is often used as an umbrella term for people whose gender identity, sexual identity or gender expression does not conform to society's traditional expectations. People who do not clearly identify as heterosexual or cisgender use the term queer for self-identification. (Cisgender people are people who live or feel comfortable and identify with the gender they were assigned at birth). It is important to note that being queer can be interpreted differently by different people, so it is better to ask how someone understands the term for themselves respectfully.
In German, "FLINTA*" is the abbreviation for women, lesbians, inter*, non-binary/enby, trans*, agender people and is used as an umbrella term including various forms of self- identification. The asterisk at the end stands for all forms of self-identification that are not explicitly mentioned here. Although the term "lesbian" is not a separate gender, lesbians are mentioned separately in the term "FLINTA to emphasise that in the patriarchal system, heterosexuality is considered the norm and lesbian sexuality is suppressed.
You can look up other terms in the "Queer Lexicon". There you will also find further explanations of terms and various brochures.