Anderson plugs can either be crimped or soldered. Most of us dont have a crimping tool sufficient to crimp this size. Can also make the plugs difficult to fit into the main plug.
Personally I find an electric iron not sufficient for the job. I generally use a butane torch.
It is also really important you use good solder, standard solder is not up to the task. You also need to dip and coat the wire before setting.