The "Other Info" tab both under "Clients" and "Cases/Projects" can be used to store additional data fields for clients and cases respectively. 
For example, if you like to store client's social security number, enter (for example) "Social Security Number" in the Field Name box and enter the value in the Field Value field. For sensitive data, check "Encrypt" checkbox and click on the Save Field button. If encryption is opted, for added security, the value of the field will be encrypted in the database. Values to be encrypted should be short (no more than 80 characters). Note, however, that an encrypted field will not be searched. 

To search clients by client field values, click on "Clients" menu tab -> Enter full or partial search word in the search box (below "Dashboard" menu tab) and click on search button. 

To search cases/projects by case field values, click on "Cases/Projects" menu tab -> Enter full or partical search word in the search box (below "Dashboard" menu tab) and click on search button.