The command to list installed packages on CentOS is:

yum list installed  

The result will be something like this:

Installed Packages  
audit-libs.x86_64  
basesystem.noarch  
bash.x86_64  
binutils.x86_64  
bzip2-libs.x86_64  
ca-certificates.noarch  
....         

To search for a specific package the easiest way is:

yum list installed | grep packageName