so that 2 speeds get added up?
You can use two connections simultaneously (load balancing). But, you cannot make it act like a single connection (Bandwidth aggregation).
If you get 3Mbps in both connections, you'll have two different 3Mbps connections which are load-balanced. When a new request arrives, based on the load-balancing logic, the best connection will be chosen. But, you cannot make it a single 6Mbps connection.