i Have to know where/when during Redistribution we have to use metric- type1;metric-type2
You would use metric-type 1 or 2 when you redistribute another protocol into OSPF.
The default metric-type is 2. In other words, if you don't specify the metric type it defaults to 2.
As you may know OSPF uses cost as the metric. Metric-type 2 would cause the 'cost' of the redistributed route to be the same on all the downstream routers. On the other hand, metric-type 1 would cause the 'cost' to increment as the route traverses from router to router.
As you can see metric-type 1 will lead to optimal routing when multiple paths exist to the external network. However, if there's only a single path to the network that is redistributed then metric-type 2 should suffice.