Look, this was an epic pump and dump. Whales are people who have lots of btc from shitting on others in past pump and dumps. They pushed the price up to a frenzy then dumped their stacks onto the masses. Basically, a few rich people got richer at the expense of everyone buying higher than 300k - which was a lot if you look at volume. It is extremely unlikely this coin will see 500k again if ever, as you have a lot of butt hurt potential buyers out of the mix. Why would whales drive it up without minnows buying? all they want is more btc so they can cash it out so they can buy bigger boats and vacation homes. Get the picture?
If you click on the highest sell price it will populate in your buy window - the amt selling is how much you can buy at that price at that time. If you want you can enter your own buy price and it will fit in with all the other buyer's prices. If you buy any substantial amount of any coin on Mint, there is a real good chance the price will immediately tank. This is because whale bts are shifting coins back and forth making it look like real people are trading, and they are looking for a sucker. By immediately sinking the price they want you to feel this was a mistake and sell it back, at which point the price will slowly start to go back up. This is the ludicrous game that is played around here, don't fall for it. If you must buy an older coin on Mintpal, wait for a pump and try to jump in on the way up - play small at first. Frankly, your odds of making money around here at this moment of butt hurt are better at the casino.

I'm not sure what you are asking, but as a newbie I want to caution you. XC just had a massive 100x+ pump over the last several days. It's way past the top, the anon function is extremely iffy and this coin is in the hands of whales who want nothing more than your bitcoin.
You've been warned, I'd look for new coins with potential if I were you.