A donation can be a gift of money or items of value to an organization but it can also be a gift with a sort of unspoken promise or reason behind it. In other words, you do not donate money to a homeless man, you give it to him. You donate money to a museum with the implication that they will continue to run and use the funds to provide access to new exhibits.
If you have a dream in which you have made a donation this means that you are thinking about your charitable spirit lately. You have probably given a donation already and this dream is here to remind you of that contribution you made. It was a good one and it was probably much appreciated by the organization that you donated to. Of course this kind of dream could also be coming to you because you think that you need to give a donation in the future but you aren't sure when you want to give that donation. Stop putting off your generosity or you will never get it done. There are people out there that could really use your extra donation and you will greatly benefit from it.
To dream that you are giving a donation means that there is something which you are really striving towards in real life and if you don't get it soon, you are going to be very angry.