According to Timatic, you are able to transit without a visa because you hold a confirmed onward ticket. The maximum transit time allowed is 24 hours.
Timatic is used by airlines to verify passengers travel document requirements for their destination and any transit.
On arrival in Dubai International Airport, there are dedicated transfer desks from which to get your boarding pass for your onward flight. The transfer desks in Terminal 3 are at Gates A, B and C.
You don't mention your carrier between Dubai and Bangladesh, so here are the airport directions on how to move between terminals.
When connecting between A, B or C Gates, all the gates are within walking distance. The only exceptions are the A Gates. For these you take the airport train.
If you are connecting to or from F Gates (located across the tarmac), your airline will tell you what to do. Services include free shuttle buses, Marhaba service and public transport.
If you’re transferring to or from certain flydubai flights from Terminal 2, you can use the dedicated transfer service. For all other flights transferring through Terminal 2, you should proceed through Arrivals to collect your baggage at Baggage Reclaim, and then transfer to your connecting terminal using public or private transport.
The airport shuttles don't have a pre-booking option; the journey time between Terminal 3 and Terminal 2 is about 30 minutes.
Marhaba is a service that can arrange transportation, and other, services which can be booked in advance.
Before arranging for transportation between Terminals 3 and 2, you should first check your onward airline's DXB information, as many provide dedicated shuttle services for their passengers.