A blockade is an act of war, carried out by military force. Saying the US is blockading Cuba is saying that the US and Cuba are at war. That alone is a pretty big reason to understand the difference between a blockade and an embargo.

The other important dimension is that countries participating in the embargo are choosing to participate in the embargo. This is distinct from a blockade which is done unilaterally. The Royal Navy didn't let ships into Germany ports during WW1 if they paid a tariff. No, they seized ships bound for Germany, because that was an actual blockade.

An embargo is when countries decline to trade with you on their own accord.

A blockade is when a country uses military force to physically stop other countries from trading with you, even if those other countries want to trade with you.

They're pretty substantially different.