This one took me quite a while to find, hopefully I'll save you some time.
If you just want to force your user to have some applications installed (e.g. 'Visual C++ redistributable') or some specific configuration (e.g. specific Windows version/ reg value etc.)
You can use 'Behavior and Logic -> System Search' add the search for what you need (file/folders/registry entries/ini files values/XML file values),
On "What do you want to do with the value?" dialog select Store the values in the property and use the property in an Install Condition".
This will cause the Search to be executed when your installation package starts and will display an error popup to the user saying what ever message you've entered for the condition.
Few notes:
- If you're looking for a x64bit registry entry - mark the "Search the 64-bit portion of the Registry" check box.
- Did not find a way to edit the Condition once created, when tried to edit it it just lets me see and change the search parameters, but for the condition it only allows to enter it from scratch; as a workaround you can save the project as XML file (Installation Information -> General Information -> Project File Format) and edit the XML externally.
Good luck.