A bit confused about testing...

Jalette
So I'm 12 weeks with my second child, it's been almost 13 years since I've done this! My question is what is the difference between the nuchal testing, Harmony, and the regular First Trimester bloodwork?
I had my panel bloodwork at like 6 weeks and FT yesterday at 12 weeks. Had US but no dating or measurements, I had those at 7 and 8 weeks.
What exactly do they consists of (the tests)? Some people are knowing their baby's gender st 14 weeks but I was told I won't find out until 20 weeks. Is that based on these tests? (Sorry so long)😝