>Can I sit maths a-level in one year - new course beginning 2017.
Yes you can sit the new Maths A Level in Summer 2018 (that's what I'll be doing), this option is designed for people who'll be doing the full further maths a level in the second year, but really anyone can do it
>Can someone please explain to me the new A-level structure
You can sit the AS or A Level in summer 2018, summer 2019 and beyond. But the AS doesn't count towards the A Level. If you want to have an A Level, you need to sit all the exams in one year. You can't sit AS in one year, and then A2 in the next year like you could before.
>My school says there is only A-levels but when i go online at edexcel i see AS and A-level maths
There are both AS and A Levels but some schools choose to not offer any AS exams, because they don't count to the A Level and are only for a stand alone AS qualification.