how can I open my Outlook on my iPad

You don't need an additional app. You can either sync your email messages to your iPad from your computer - instructions are in the user's guide as well as here:

http://support.apple.com/kb/HT1386

or you can set up your iPad to connect directly to your email provider - instructions also in the user's guide and here:

http://www.apple.com/support/ipad/mail/

If your email service is an Exchange server, I'd recommending setting up your iPad to talk directly to the server. Then your mail, calendar and contacts, if you wish it so, will synchronize automatically without you having to sync with your computer.

Regards.

The built-in apps will work fine with Outlook. You can configure it directly though iTunes (click on the device, then "Info", and you should see options to sync Calendar, Contacts, and Mail with Outlook - if your Outlook account is set up on the same computer.

Alternatively, you can go directly on the iPad into Settings -> Mail -> Add Account and add the account, but you'll need some specific information for your email account (server names, etc.).