It depends on how many mg/ml the medication is.....if the medication is 10mg/ml then you would give 1ml.....if the medication is 20mg/ml then you would give 0.5ml to = 10mg.
mg stands for miligrams this is a measure of weight while ml stands for mililiters, this is a liquid measure.
10mg of one substance, say water, would be a different amount of ml than lets say another substance, like a liquid medication, like amoxicilin. That is because water and amoxicilin have different weights and therefore the one that weights the most would have a lower amount of ml than the one that weights less.
Also, no one should be giving injections unless they have been properly trained and are doing so at the direction of a prescribing healthcare provider. There is significant risk by untrained people giving injections including, but not limited too, infections, use of dirty (non-sterile) needles which can transmit blood-born pathogens like HIV and Hepatitis, injecting the needle too deeply possibly causing doing muscle/nerve damage, ect...