Well. Being LGBTQ+ is not a choice. Being an ally, which is a part of the community, is.
You know if you are LGBTQ+ if you are born intersex, that one is easy.
If you are a gender other than your assigned sex, you are transgender. Which is what the T stands for.
If you like the same gender, no one, or more than one gender, you are one of the certain types of sexualities/romanticities we have.
If you have no idea what you are, but know you are not cishet (cisgender, hetero), then you are queer, which is what the Q stands for.
If you are cishet, but still supporting, you can be part of the community by calling yourself an ally.