If the price is at 100 and you wish to buy it, there are 3 methods for entry.
1. So in the rising market, if you wish to enter the market you can hit market order and you will be in around 100, or 101 or 102, depending on the market and how liquid that market is ie. in less liquid markets you will encounter slippage.
2. However if you wish to enter the market when price reaches 105, that you place a stop order at 105 and when price crosses that, your order is filled, in this case you are waiting for the market to prove itself, that there is buying momentum.
3. If you are not happy to chase the market but think there is still more upside, then you wait for retracement below 100 to say 95 and then wish to enter, in this case you place a limit order at 95, when the market hits that or 94 you will be filled. Ofcourse the risk here is that market may just keep rising from 100 without retracement.
Hope this helps