Write to eMMC boot0 partition from u-boot

Question

I am using eMMC based on 5.1 Version, which has boot0, boot1, rpmb and userarea.

Inorder to write to eMMC from u-boot, mmc commands can be used.

mmc read commands is of below form.

$mmc read addr blk# cnt

if i give blk to 0x0, where it will write boot0 partition or user area ?

Thanks in advance