yes, you can put 2 sims in the slot instead of a sim and an SD card. if you do then you have a choice of sim 1 or sim 2 to send message. so that explains the blue box
It is because some of the S7 edge models are dual-sim. You can choose to have a single sim and a memory sd card or dual sim. The blue box 1 is telling you which sim. I think this changes to 1 and 2 when you are in dual sim mode. I have not tried it.