Server Pools allow the same functionality of logically dividing the cluster into small segments that can be used for varying workloads.

But unlike the traditional mechanism available up to 11.1, which only allows this task by choosing the instances to run on nodes as Preferred & Available and running services using the same architecture, server pools offer a much larger list of attributes which help in the management of resources in a rather simple and transparent way.

In server pools, the underlying hosts of the cluster are added (and removed) from the pools much more on-the-fly, and take the burden off the DBA’s shoulders for this task. With just a few parameters to take care of, the whole stack becomes much easier to govern and administer, while still being completely transparent yet powerful to manage all the types of different resources in the RAC clusterware environment, especially when the number of the nodes go beyond two digits.

Server pool is configured by 3 attributes called minimum number of servers in pool as MIN, maximum number of servers in pool as MAX and importance of various pools as IMPORTANCE.
Using importance parameter you can ensure that low precedence workload doesn't eat up more resources. Clusterware can move servers from server pool robotically to maintain important server pool configuration

For adding server pool using srvctl command you can check help of utility as follows.
[root@rac2]# srvctl add srvpool
Adds a server pool to the Oracle Clusterware.

Usage: srvctl add srvpool -g [-l ] [-u ] [-i ] [-n " "]
-g Server pool name
-l Minimum size of the server pool (Default value is 0)
-u Maximum size of the server pool, -1 for unlimited maximum size (Default value is 0)
-i Importance of the server pool (Default value is 0)
-n " " Comma separated list of candidate server names
-f Force the operation even though some resource(s) will be stopped
-h Print usage