Your voucher will have a voucher code and a security code, which can be used to book online.
Just go through the booking process as usual, and during Checkout you will reach a 'Review' page where you can redeem your voucher/s. Enter the voucher code and security code and click 'Redeem' (you may need to click this button multiple times, depending on your voucher type and booking type - some vouchers will be applied to one space each time they are redeemed).
If you have more than one voucher, you can delete the codes after the first voucher has been redeemed, and then enter and redeem the next set of codes.
You should then continue through the Checkout process and complete your booking. Once this has been completed, you'll receive a booking confirmation email. These often go into junk mail folders, so please check there if you don't see it!
Visit www.mendip.me/myvoucher for various links to activity calendars which will list only the slots for the activity that your voucher type covers.