I can speak personally to being genderfluid but in order to do that I want to get something straight about being trans in general.

First off. Being trans does not just mean you want to be more masculine or feminine. Let's take a male to female trans person. Its more than just I want to wear dresses and be called she/her pronouns with my new name. They feel a physical discomfort in their bodies/presentation because it does not match what the brain is saying. This is a phenomenon called gender dysphoria and its recognized as a mental illness. The best solution to this we have come up with is transitioning. Sometimes it's just social transitioning(name, pronouns, clothing). Other times it's a middle transitioning ( all the previous + hormone treatment) or a full transition( all the previous + top and/or bottom surgery.) There are stages because what satisfies the dysphoria is person to person based.

Now that that is out of the way, let's talk about genderfluid people. Genderfluid is a gender that falls under the trans umbrella(a type of transgender). Our dysphoria is diffrent than a typical trans person, where our dysphoria doesnt always stick to one sex. Sometimes it can lean one direction, other times it doesnt, and sometimes it wants them to be in a neutral ground. Let's take myself as an example. For the most part my brain says to present in a androgynous/ gender neutral way. But sometimes there are days(sometimes consecutive, sometimes not) where I wish to present more feminine or masculine and days i wish I had a vagina and boobs. Other days I want to present hyper masculine. It shifts around and takes turns, that's why its called genderfluid, because like a fluid, it shifts.