If trans women are female then why say trans?

Because there are unique oppressions and experiences people face for not being what they were assigned at birth. We need language to describe these experiences and oppression. And, much like black and white women have different experiences, so do trans and cis women. Intersectionality is important, it’s important to recognize what makes us different. 

what makes some female?

Being women, knowing yourself to be female, etc.. If you need a more comprehensive answer, I have one here 

What makes someone trans?

Knowing themselves to not be what they were assigned at birth. That’s it.

I saw this one post that said “Not all women are female and not all females are women” I thought that made sense but idk, thanks

That’s a commonly used phrase from liberal feminism’s stint where they thought separating gender and sex as two supposedly unrelated entities (which they are not) was a good thing.  It still posed sex as a biological reality instead of the social construct it is, and we’ve long moved past that, and feminism is catching up. 

That said, that phrase can still be accurate. There are some trans women who reject the label of female, and some NB folks who reject the label female, yet remain women (or women-aligned). There are also some trans men who consider themselves to be female, and some NB folks that, regardless of their gender (or lack thereof) consider themselves female. That’s their right, and with sex being a subjective social category, there’s nothing technically wrong with that. But the phrase was largely in reference of the cissexist theory that trans women were male, trans men were female, and NB folks were esssentially what they were assigned at birth, and that’s not anything worth supporting if you’re a trans ally, given cissexism is at the heart of our oppression.

If you want a better read on why sex is a social construct, the link above would work, but so would this, or this