IF "New Client" means clients that have been recently added to your system, you will need to use the "Entry Date" filter to get a list of your newly added clients:
IF "New Client" means clients that have been assisted (have an assistance record) for the first time, you can use the "Assistance" report and select "Only include cases assisted for the first time since start date".
Otherwise, the "Report Summary" section will give you totals on "New Cases" and "New Households".
Choose to include a total for "New Case Count" (number of new clients served) and "New Household Count" (number of new households served) -- See screenshot here:
These are simply the totals for those clients/households you served for the FIRST time within the date range you chose to report on (quarterly, monthly, weekly, etc.) -- See screenshot here:
Notice: Of the "Total Cases Assisted (6)", 3 of those are "New Cases". And of the "Total Households Assisted (4)", 1 of those is a "New Household".