Get website hosting (eg: a $20/mo Linux+PHP5 website hosting account from here: http://mediatemple.net/webhosting/shared/ - or any other PHP5+Linux+MySQL hosting account)
Decide where you want the system installed (eg: admin.yourwebsite.com or yourwebsite.com/clients/ )
Follow the UCM installation instructions (available here) to install UCM in the desired location
After installation enter the email SMTP details and click the "Test" button to make sure UCM can send emails successfully.
Check automatic updates will work, go to Settings > Upgrade and enter your item purchase code. Check back here from time to time to get the latest features and fixes.
Setup the CRON job (go to UCM Dashboard and click on the "CRON Job" notice for instructions) the hosting provider can assist with this.
Change the default Administrator account details by going to Settings > Users - change the email address and password
Log out and log back in using your new details to be sure it all works.