I have to make a ext4 and swap partitions and set "/" to path for ext4
What sizes should the drives be?
After that I use Raw Harddisk Copy to copy the nvOC img to the ext4 partition.
Is that it? Do I have to make bootmanager or what it's called?
You don't need all that: the nvOC img file is already a full partitioned image, including the bootloader; you just need to use HDDRawCopy, as instructed in the OP, to flash it in your USB stick. Don't need to do anything else, after a successful flash it should boot right away.