Does all the money that a donor gives to an NGO go directly on its projects and beneficiaries?

Think of an NGO or charity as a social business. In the same way that a business needs money to operate, so does an NGO. These days many NGOs require professional, skilled staff who provide skills and expertise in a variety of areas that relate to community development. 

These roles may be back-office finance roles that require skilled financial management; there may be safeguarding experts; there may be youth workers and there may be important leadership and management roles or other specialist areas such as health. 

At the end of the day, all NGOs need to have some income to cover these costs and so usually, a percentage of a donation or grant is allocated to such support costs. This typically may be in the region of 5-15% of the donation, with the rest of the donation directly on project implementation.  

Even NGOs that are run completely by volunteers will have some overhead costs. Most donors are understanding of this situation and it is always good to be transparent about how money is spent, in Annual Reports which can be sent out or made available to any donor.