Doblo Doblo Multijet Coolant Change

I couldn't understand everything. Some terms and position of some parts from pictures were dizzy for me. Could be more elaborate but with first grade terms. For example, he said : "dont open the lid of the expansion bottle when the engine is hot". Well, i did that alot and when still running. Did i damaged the water pump, or some hose, or even the engine block? I wanted to know. But he didnt said.