I’ve conducted handfasting. It’s just a marriage ceremony. It’s outside of formal religion but over the last 300 years the vast majority of handfasting has been for Christians. It’s more usually Pagan now. The handfasting ribbon or tie joins the couple just as the priest’s stole (blessume) is sometimes used in church.
I ask the couple to provide it as something meaningful to them.
One difference between a conventional marriage ceremony and a handfasting is that the couple can set a time limit if they want. Traditionally it’s been “a year and a day” so the union has been tested for all seasons. The “day” Is simply a period of reflection as to the next step. I’ve never conducted a time bounded handfasting.