Canvas FAQ: Ask Questions

Hello everybody! Often in the comments and in PM , questions arise about the Javascript Canvas.
Most, even if they have theoretical knowledge, are corny lacking experience.
I have this experience. Therefore, in this thread I propose to ask questions about Canvas, to which I will answer the following topic.
If there is no reg on Habré - you can throw off your questions on shocksilien@gmail.com, I will add it to the topic.
Initially I wanted to throw in q & a, but the number and quality of questions in the comments to this topic will positively affect the quality of the next topic, so I count on your support)

ps. Feel free to ask those questions that you think are stupid. If they interest you, ask them.
pps I will ask clarifying questions. For example, "for what purpose?" This does not mean that the question is wrong. This means that, depending on the goal, there may be different solutions.

The answers