Generally there is much more information required to advise you propperly on the issue.
- What Operating System are you using, Is the application designed for the specific environoment
- Do you get an Error trying to start the Setup, if so what does the error prompt you with?
For starting with downloading and installing Lightroom you can begin with downloading the latest version:
* Now for the iPad version you need to have a Membership for Lightroom and not a Perpetual License.
When you have Downloaded and Installed the Application (Desktop version) You need to create first a Catalog at the first launch.
Without a Catalog you can't use Lightroom. This is prompted when you first launch the application. When you can't create a Catalog
(Due to permission problems on the system) This should be fixed.
Please eloborate the problem you exactly are experiencing, so we can assist more accurate in the problem.