There are two fundamental order types: Market Orders and Limit Orders.
If you enter a BUY market order, you will pay any price, as long as you get the liquidity NOW! If you enter a BUY limit order, you limit the price you will pay at the risk of not being filled.
Let's say the stock is offered at $110 and you desperately want to buy it - at any cost! You would enter a market order and it may be possible that you pay $110, $111, $112, or $115 - but at least your order will get done. Note that if really wanted to buy the stock at $100 and you entered a market buy order, you entered the WRONG order and would still be buying at +$110.
You say to yourself, I like the stock, but I don't want to pay more than $112. Instead of entering a market order you enter a BUY $112 Limit order. Since the stock is being offered at a better price ($110), you will immediately start getting filled, but if you impact the price, you will not pay higher than $112 - as such, there is a chance part of your order is not filled.
If you wanted to buy the stock at $100 instead, all you do is enter a BUY $100 limit order - and then wait for the stock to price to get to $100.