Simple words for someone who is grieving

I lost my brother when I was 17 and I know for a fact there's nothing you can say to make it better. I stumbled across these words somewhere and wrote them down, they say it best:

I don’t know your grief, but I know grief. I’m here for you.

Also, if you are wondering if you should write a card or note, just go ahead and do it. It's not weird or strange even if you barely know the person, trust me they will appreciate it.

Much love.