Hi Snehil,
You cannot connect Physical Conserving ports shaped as squares to Simulink signals shaped as arrow heads.
To learn the differences, consider taking the Simscape Onramp. It is a short, hands-on free tutorial.
Moreover, I see that you are modeling a three-phase voltage source converter. This topic is covered in detail in the Power Electronics Control Design course I authored and it is regularly offered in many worldwide time zones (see calendar). The latter one is a paid service - you find pricing in the schedule as well.
Hope this helps,
Antonino
