Hi,
Lets say I want to buy bitcoin for 10USD. Do I have to pay 6USD as transaction fees? How do you trade really small values of bitcoins?(Withdraw from one bitcoin wallet to another?)
No. It surely isn't 6$. There might be some services that charge that much, but it really isn't needed. To check how much fees you need to add, use
https://bitcoinfees.21.co/to get the right sat/byte. Also if your tx has no priority, you really don't need to add a 180/b fee.