A memorial ceremony takes place after the funeral. It's a chance for more people to commemorate the person who's died, in a more informal setting. It may be more of a celebration of their life, though of course it's also a place to mourn.
You could have the memorial soon after a private cremation or burial, or some time later, when you feel more sociable. It can be in your home, in the open air, in a venue you can hire and decorate. There are no time constraints (unlike funerals), so you can include have more people speaking, maybe a slide show, even a recording of the person who's died.