Demonstrate Basic Respect to People Regardless of Identifiers
Just because "transgender" can be used as an umbrella term, does not necessarily mean people want or can afford medical or surgical interventions. It also does not mean that the person uses the term to define how they feel about themselves. They may not want to be identified as transgender by other people. In many cases, this is a safety issue.
So, although it may be human nature to be curious, being respectful means respecting people's privacy. Do not ask people about their status (although asking about preferred pronouns is typically OK) or whether they plan to have surgery. Give basic dignity and respect. Also remember that surgery (or the lack thereof) is not a qualifying factor for how someone chooses to define themselves.
Exploring things like presentation or roles that have a huge social gender component, such as taking care of the home, is difficult and can have very real consequences even when someone identifies as cis male or cis female. Exploring gender identity at all can have immediate as well as far-reaching consequences, from threats to physical and emotional abuse, withholding of medical treatment (whether related to gender or related to anything else such as the flu or a broken leg), isolation from friends and other support networks, loss of employment, and more.
If someone introduces themselves to you and says their name is Kyle, but you had heard their name was Kelly, this person is telling you their name is Kyle. Just go with it.
The terminology around gender is always shifting and it's something worth keeping an eye on. For certain terms, such as gender queer and gender fluid, the differences can be up to that individual. Regardless, it is not your place to try to "correct" someone on where you think they fit.
Also, just because someone you read as masculine is wearing nail polish or certain items of jewelry or wearing bright colors does not necessarily mean they are avoiding prescribed gender norms or that they are transgender. Different communities have different norms. In some communities (especially communities of color) people who identify as men wear brightly colored clothing that may not be seen as appropriately masculine in other communities.
Trevor Project also has a resource center aimed at youth and allies. While Trevor Project is known for being a help line and website for LGBTQ+ youth in crisis, their additional resources may be helpful for understanding the concerns of the LGBTQ+ community and how children and youth may get bullied at school, threatened, kicked out by their parents, sent to conversion therapy camps ( which are illegal in some states), and more.
The National Center for Transgender Equality also has resources ranging from state reports on discrimination to information regarding how health policies and laws may affect transgender or gender non-conforming people, from ID regulations to passports to workplace discrimination and potential resources.
If you have an LGBT community center near you, talk with them about resources. Not just in terms of health resources, but also what your neighbors are concerned about: whether it's safety walking down the street, interpersonal/relationship violence, refusal of medical care, discrimination in the workplace or in finding apartments/housing, the complications of name changes, or more.