Trans people are individuals who strongly feel that they are, or ought to be, the opposite sex. The body they were born with does not match their own inner conviction and mental image of who they are or want to be. Most people were painfully aware of their gender incongruity from early childhood, while others become aware in early to late adulthood.
Trans identity cannot be attributed by others! It is your own deeply held conviction and deeply felt inner awareness how you identify on a gender spectrum. Trans identity is private and internal. It is felt, not seen. It cannot be deduced from how a person looks, moves, dresses, or behaves. The only way to know a person's gender identity is if they tell you!
Gender non-conforming people are individuals who do not adhere to society’s rules and social constructs of gender expression. A term comes from the concept of non-conformity, as in not following set rules defined by majority. A gender non-conforming person may choose to present as neither clearly male, nor clearly female, but rather as a gender-free individual or somewhere in between.
Non-binary is both a gender identity and a catch-all term to describe gender identities other than commonly socially constructed binaries of male and female. Some of the common non-binary gender identities are:
Agender: Someone who identifies as without gender, or to whom gender does not feel like a salient concept. This is also sometimes referred to as being gender-free or non-gender.
Bigender: Someone who has two genders.
Genderfluid: Someone whose gender moves around, either along the female-male binary or outside of it.
Genderqueer: Someone who typically rejects notions of static categories of gender and embrace a fluidity of gender identity.
Most trans people view transition as some form of physical body modification via hormones and/or surgery. People undergo this process in order to fully live as a different gender than the one assigned them at birth, modifying their bodies to match their internal sense of who they are.
While there are people who view transition as a set of stages, I believe it is a non-linear process. I view transition as a process that results in a paradigm shift in how a person experiences gender, regardless of whether they end up transitioning physically or not. Every step of the way, I encourage you to check in with yourself. Is this enough? The path of transition is not linear! Nor is it a "cookie cutter" one-size-fits-all process.
The key question is "How do you want to live your life?" and "Have you gone far enough with your transition to be happy with your gender identity?"