How to start?

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Topics are question threads like "How to start".
Posts are comments like this one under a topic.
Discussions and Questions are just types of topics.

There are 2 kinds of topics - questions and discussions.

Questions are apt to have one best answer, and have a way for the person who asked the question to give a red ribbon to whatever poster answered the question best.

Discussions are more open ended with many thoughtful replies being possible.

I'm not sure if it is still true, but questions may have a relatively short term history in the forum archives, in contrast to the discussions.

Posts are individual responses to topics or discussions, or even the "starter" topic post, such as your "How To Start?"