Market orders: speed over price
A market order fills immediately at the best available price. You're guaranteed to get in (or out), but not at a specific price — in fast or thin markets the fill can come in worse than the last quote. That gap is called slippage.
Use market orders when getting filled matters more than the exact price: exiting a position quickly, or entering when you've decided the level is good enough. Market orders are usually charged the higher 'taker' fee because they remove liquidity from the book.
Limit orders: price over speed
A limit order fills only at your chosen price or better. You control the price, but there's no guarantee it fills — if the market never reaches your level, the order just sits there.
Use limit orders to enter or exit at a planned level without watching the screen, or to avoid slippage on larger size. Because they add liquidity to the book, limit orders often earn the lower 'maker' fee.
Stop and stop-limit orders
A stop order is dormant until price hits a trigger level, then activates. A stop-market triggers into a market order (guaranteed fill, possible slippage); a stop-limit triggers into a limit order (controlled price, but it can miss the fill in a fast move).
Stops are how you automate risk: a stop-loss exits a losing trade at a pre-set level, and a take-profit locks in a winner. Decide the trigger before you enter — not in the heat of a move.