You can buy a Banglalink sim card in 2 ways
1. Order online (Online purchase)
and  2. Buy from shop (Retailer point and Banglalink customer care)
Now I’m telling you
How to buy a sim card from online?
From Now on, you can buy your desired SIM Card or connection from your house.  you can choose your desired number from thousand number by a single click of your laptop or computer button.

1. To buy Banglalink sim from online go here and follow the instruction. 
2. To Buy GP Sim Card from online Click here  and follow the instruction
3. To Buy New Robi SIM Card from online Click here  and follow the instruction
4. To Buy New Airtel SIM Card from online Click here  and follow the instruction

What do you need to buy SIM Card? 
To buy your SIM you need (citycell, teletalk, grameenphone Robi, banglalink, Airtel )   
1. 2 PP size Color Photo
2. A Photo Copy of NID Card
3. The Real person who will buy SIM Card because his Finger Print needed. 

So go to a Retailer point or Customer Care of your desire sim card with your 2 PP size Color Photo and  A Photo Copy of your NID Card.

Thanks for the questions.