What is Charity/Donation: To give happiness to other living beings, humans or animals. When you give happiness to others, you will get happiness in return. Despite of giving away your own belongings, you feel good because you have done something good.
When would one experience unending happiness? It will happen when you let go of the one thing in this world, which you love the most. In worldly matters, what is that? Money. People have excessive affection for money. Just let it go and let it flow. Only then will you find that the more you let go of it, the more it will come to you.
Param Pujya Dadashri (master of spiritual science) has given extensive information about giving charity/donation, and other questions such as what is charity?, what are benefits of charity?, what are the types of charity?, where(To whom) should charity be given?, how to donate? What is anonymous charity / donations?,... and much more.... readers will surely find this invaluable and insightful.