Great image pulled down by Business Insider that shows how desperate they were to keep the price at or above the offering price of $38 a share. Losing money on the first day of trading would have been a huge embarrassment. The stock closed at $38.23.
On the left side, you see the "bids" that are in the market for the stock. Those are the offers to buy. On the right you see the "asks", which are asking prices by sellers. Note that next to each bid or ask there's a "size" which is the size of the offer to buy or sell. Note two things: At the top of the left column, you see lots of bids at $38.00 on various trading platforms. (The BATS exchange, Arca, etc.). What's more, the size of those bids are HUGE. Hundreds of thousands of shares compared to relatively tiny asks and bids everywhere else.