Most people who are assigned female at birth identify as girls or women, and most people who are assigned male at birth identify as boys or men. These people are cisgender (or cis).
Some people have a gender identity that doesn’t match the sex they were given at birth — for example, they were born with a vulva, vagina, and uterus, but they identify as male. These people are transgender (or trans). Transgender is the “T” in LGBTQ.
Trans can also include people who don’t identify with strict male/female gender roles. Other people who don’t identify as either male or female call themselves genderqueer. There are other gender identity terms and labels, but don’t use terms like transgendered, transvestite, tranny, or, he-she — they’re old-fashioned and can be hurtful. It’s always best to respect the words people use to describe themselves.