hi Zivaah
Following steps should work for you:
1) If you don't have enough Lindens to buy Kitty Dollars, you can purchase lindens on the SL website: https://secondlife.com/my/lindex/buy.php
2) Login to SL with Radegast at a place where you can rez items (your home?).
3) I have offered you a cattery dock in world. An acception dialog should show up in Radegast when you login.
4) Go to "Inventory" in radegast. Find the cattery dock you just accepted (on top of your objects folder), RIGHT CLICK it, and select "Rez inworld".
5) The cattery dock will ask you to grant rights to take Linden dollars from your account. Grant them.
6) Go to "Objects" in radegast. you will see the cattery dock listed there. Click the dock name.
7) Click "Touch/Click" in the right upper menu. the dock dialog menu will pop up. Select "Add K$", and choose your value. You now did buy Kitty Dollars!
8) Log off from SL, login to your cattery, and buy the food there.
If one of the steps fail, just let us know.
Regards
KittyCatS