vCenter Operations Manager Enterprise (vCOPs Ent) can be part of vCenter Operations Manager Enterprise Suite, which includes vCOPs Ent, Infrastructure Navigator, Chargeback and Config Manager or is sold separately.
There are two versions of vCOPs Enterprise - vApp and Standalone.
Standalone version is intended to monitor not only virtual infrastructure, but physical environment as well and it is always part of Suite. If you have license keys with Servers or Workstation or Terabyte or Network Device description, you have purchased Standalone. vApp version can be part of Suite and is dedicated to monitor virtual infrastructure only. It is licensed per VM, no matter if they are workstations or servers.
Standalone version is installed on Windows or Linux machine. It requires commercial database such as MS SQL or Oracle - please, have a look into VMware Product Interoperability Matrix.vApp version uses Postgres SQL bundled within the vApp which makes installation process quite easy.
And last but not least, if you don't plan to monitor physical infrastructure and want to use Suite products (ie. Chargeback, etc), you can use vApp, too.
All documentation is published on VMware's website - go to http://www.vmware.com/support/pubs/ and find the docs for particular product. In case of Standalone version, I strictly advise to RTFM because whole suite requires apropriate planning and sizing.
I hope it helps.