Whether you need a women specific geometry or not depends on your body type. Womens bikes are often built to fit riders with long legs vs. a short torso. There are men who need that specific geometry too, and there are women who fit well on a mens bike.
I am not tall, but ride a mens bike (in small size) with no problems. If you have trouble finding womens bikes for your size, but would need a womens geometry, you can still do a lot by for example changing the seat post and stem.
It's best to find a good bike shop and testride some bikes. They should know which bikes could fit you and how they can adjust them to your needs.
Generally, mountainbiking is very much learning by doing. No other mountainbiker has ever mocked me for being clumsy, and many have been very helpful when I started riding.
In the beginning I learned a lot by practising skills in empty parking lots. Some sort of bike clinic can do a lot for your skills too, it helps if someone can tell you what you are doing wong and how to correct it. There was another thread not long ago where some women talked about their experiences in one of those bike clinics.