Burp it a few times to get any air out of the system. Run it until fully warmed up, let it sit until cold and check the level in the radiator. Top up as necessary, repeat until no more coolant is required. If you have an overflow tank that is designed to pull the coolant back into the engine as it cools off, make sure you keep the level at least at the minimum when cold to keep it from drawing air back in as it cools.
100% antifreeze has less heat transfer capacity than a mix. I find 20% antifreeze is about right at least for the warm seasons.