The metformin is so your body can use the insulin better as you are insulin resistant.
The second one persuades the pancreas to produce more insulin. (I am fairly certain but stand to be corrected)
My mum is t2 and on insulin and both of the others you mention. I had no idea what all the meds did until I was diagnosed myself. Luckily, I'm only on metformin and managing mainly through diet.
Out of interest, what were their reasons for starting you on insulin? I presume your body just isn't making enough of it's own?