It is completely natural to be at a loss for words. You can’t fix the situation, rationalise it or explain the loss, and it’s not uncommon to feel worried about saying the wrong thing.
It is one of the most difficult times in anyone’s life, and the most important thing is to let the bereaved know you care and that you are there for them if they need you.
Some people suffering from loss like to talk to others who knew the dead person. If you knew the person who has died well enough it may be comforting to share your favourite memory or photo of them.
Just listening to the bereaved person is often enough, allow them to talk and express their emotions without offering opinion. Avoid saying "I know how you feel" - each person's loss or grief is different to them.
You could say;
People experience loss and grief differently. There isn't a time limit. Grief isn't a process to go through, the bereaved person will learn to adapt to a life without the person they knew and cared for. Grief lasts much longer than most people expect. Your bereaved friend or relative may need your support for months or even years.