Before giving Donations to temples/trust you shud first ensure that the said temple trust is covered by the provisions of section 80G of the I-T Act. When you donate the said institution gives you a receipt for the donation made whihc is proof that you ave hte donation. On the receipt itself it is written that donations made to the trust temple are exempt u/s 80G of the Income-Tax Act.
the donations made are either deductible 100% or 50% as teh case may be from the taxable icnome. However the total donations shud not exceed 10% of the Adjusted income after considering the deductions undet other sections apart from 80G. Suppose if your Gross income is 500000 & the deductions u/s 80C are 100000, then your qualifying amount for donations would be 10% of 400000 whihc is Rs 40000. So if the applicable deduction rate is 50% then the maximum deduction that can be availed u/s 80g would be Rs 20k.