When you have enabled the ‘Case Deflection’ option with the selection of Category, your customers can search for a solution by inserting the keyword or a sentence related to their queries/issues by logging in to the portal.
Your customers will be able to see the list of cases by clicking on the Case module.
After clicking on the + Add button , your customer can find the probable solution by searching the query/issue. The search result will appear as per inserting the search keyword.
The customer can also print the solutions by clicking on the ‘print’ icon. 
If your customers could not find any probable solution or if they found a solution but it is not relevant to what they were looking for then they can add a new Case. 
Note: If You have disabled the ‘Case Deflection’ option in SuiteCRM, the customers will get directly redirected to the above page to add a case. They will not get the ‘Search Solution’ option.