Thank you all !!

I understand more now and know that I should learn and exercise with smaller amounts.

I still have these two questions . I would appreciate if someone can answer them.

How can you make money on cex.io if for example 1Eth costs you 800$ but to sell back 1 Eth you only get 700$ back ? Even if you buy low and the price increases by 100$ you would still only break even. Actually it should move up even more up because of the fees.

What exchange sites would you recommend ?