Hi, Is bitcoin legal in Bangladesh?

As, I am new here, please advise me, how to start.

No, Bitcoin is not legal in your country. I also read about it at this link https://en.wikipedia.org/wiki/Legality_of_bitcoin_by_country_or_territory and it clearly states it is illegal to use bitcoin in Bangladesh .So, I will advice you should only read about this technology and should not invest or indulge in any type of trading related to bitcoin. There are few links which might tell you that even bitcoin mining is legal in Bangladesh but I think even if you earn bitcoin in any ways, there might be no ways for you using it to convert in local currency. But you can use bitcoin to buy stuff online but that too involves high risk as if you get caught you may need to face serious punishment.