I want to start writing

[Kml1987]

I have all these ideas and scenes in my head I don't know how to put them on paper. I love reading but I also would love to write. But no idea where to start.

Just write! All you need is a pen and paper. The key thing about being a writer is that you need to get on with it.
As soon as I was published, half the people I knew told me they really wanted to write and had a great idea for a story. But you can't be a writer if you don't write. The more you do it, the easier it becomes. It doesn't have to be for other people's consumption. It doesn't have to be any good.
If you're really struggling for ideas, maybe an adult education class might get you going. But if you already have ideas for scenes in your head then why not start with those? What is stopping you from writing them down?
I'd recommend Bird by Bird by Anne Lamott.
Good luck!

I have a rough document where I pour out anything and everything that comes to mind, then filter it until I have an idea of where I'm going for the next few chapters. It's hard, especially making dates and times add up, but its incredibly satisfying when you read through your draft knowing that you can now chop and change as you see fit.

There are all sorts of types of writing. there is a huge market for micro (under 50 words) and flash fiction ( under 500). Short stories are quite easy to get published in literary journals too, and most seem to be under 1500 words , with a rare few that go to 5000. You will likely not get paid for this, but the confidence boost is well worth it.

Get a twitter account. Follow some literary journals. Riggwelter press, Cabinet of heed, Jelly fish Review, Flashback Fiction......every time you add one, it will suggest other similar friends and so is the best way to find out about monthly deadlines, themes etc. BBC writers room has an excellent free script writing resources. if you have a gift with dialect it is actually quite easy to get into with high turn over shows such as Doctors and Hollyoaks.

@schmalex is correct though, to be a writer, you need to write. You need to purposefully carve time out to sit down and even of your brain is blank you need to just get on with it.

The way I write, is to just write out exactly what I am thinking in my head. No matter how bad it looks on paper I keep going so I can get the story out. Full on And then he said "blah blah blah" and then I replied "ho hum" and then he (did an action)

I go back over it after a couple of chapters and structure it. I call it my brain vomiting a storyline that can later be edited into something beautiful.