Im new here and i just want to ask a question..
Welcome aboard. We all will try our best to help you with your queries.
Does bitcoin exchange rate varies from time to time?
Yes, and it's not just limited to the value that varies every second on just one exchange, it varies from exchange to exchange based on the trading. It's because of the nature of Bitcoins that it's not stable at a fixed rate and can be sold at any values (that we prefer).
If so, when is the best time to convert bitcoin into money?
It depends on your decision, because the best time according to me is when you really need fiat on hands.
Is it necessary to just save all the bitcoin and trade or use it after several years?
No, you don't really need to. But I believe that holding gives great rewards than selling immediately.
Do you eat the seeds? No, right? You sow them, reap the fruits after waiting for some quality time to get the sweetness that you expect.