So I own $1000 in bitcoin but I want to invest the remaining amount to accumulate a whole bitcoin. The prices fluctuates every second so how can I do this on coinbase? I believe this is called a market buy order and I've looked at the steps on how to do this but I think they're outdated or wrong.
Your available $1000 in far below the current price of bitcoin. The volatility of bitcoin won't allow you to purchase at such a price for a whole bitcoin. But if you are a professional trader, you can use the $1000 to trade with Alts that has a good market value, or better still invest in prospective projects IEO or ICO then will you be able to own a whole bitcoin in respect with time. Don't feel discouraged with the turn out of some previous Alts. Check the signature which I wear, you may prefer investing in it.