Question: What the steps to follow immediately after installation to make sure the existing data is available for search?
1. Admin -> Setup -> Enhanced search -> Optimize (only if using Enhanced Search)
2. Tools -> Rebuild Caches -> Rebuild Thread Fields - indexation of all existing thread fields into a separate MySQL table
3. Tools -> Rebuild Caches -> Rebuild search index - select Custom thread fields as content type and rebuild.
4. Admin -> Forums -> Custom thread fields -> [Edit a field] - check Allow Filter checkbox if you want the field to be shown in filters.
5. Admin -> Forums -> Nodes [Edit a node] - setup the fields to be shown in thread list directly under "Show in Thread List".
Check product description for more details about features available in the product.