I am guessing since this is in the budgies forum that you do have budgies correct?
The treat easiest to get your birds to accept would be a piece from a millet spray.
To get your birds used to the treat first hang a bit of it in the cage (not a full spray just a section for them to get used to and try). Once they seem to eat or pick at the one in their cage try holding one though the bars of their cage and wait patiently for them to take it. If they have never really had human contact or been handled you will have to be very patient for them to get used to a treat. When they will eventually eat it while your hand is outside the cage holding it, move to the next step. Open the door and place the millet in the palm of your hand. Wait patienly (even while they flap around or screech) until they calm and will come check out the food in your hand. Then you can work with them being out of the cage and coming for a treat (in a small closed room).
After saying that if your birds will come to you or perch on your hand etc without a treat then there is no reason to offer a treat. Praise will work wonders. There are many quick ways you can tame budgies to be handled but many of them will not get them ready to work (train) they will just become used to being held and sometimes will revert back to nipping/biting at later dates. By gaining your birds trust through patience you will have a lasting relationship with your bird.