A market order says: trade now, at the best price currently offered. You pay the ask to buy, or sell at the bid. The spread is part of the cost.
A limit order says: trade only at this price or better. It can wait, and it might never fill.
A stop order is usually the exit you wrote in advance, at the place where the idea is wrong. In a fast market the fill can be worse than the price you chose.
Write the instruction before you need it. The free class is a place to walk through one example out loud.