Redistribution is the technique to distribute one routing protocol into another. If you have two routing protocols, you can mutually distribute them into another to garanty reachability.
There are many possible scenarios for redistributiong one protocol into another one.
You could simple remember that there should be given a metric for the redistributed protocol. So if you want to redistribute rip into ospf for example, you must give a metric value when redistributing.
Redistributing from rip into ospf means, that on an ARB (area boarder router), where two routing protocols are running, you make the routes from each protocol usable to the other routing domain and vica versa.
router rip
redistribute ospf 1 metric 1
Here it means that you send all routes that are running under ospf process 1 to rip with a metric of 1.
So now the rip routing domain has all routes from the ospf domain also available.
To redistribute the other way:
router ospf 1
redistribute rip subnets metric 1
This will send all routes from the rip domain into the ospf domain under ospf process 1. It will also redistribute all routes with a metric of 1 and all subnets.
It’s very important to set the metric. If you don’t, you will not see any routes on the other side.