The board publishes no conversion rate, so points-per-vouch is yours to set. Watch what one vouch actually moves your score by, then dial it in.
Vouching happens on X. You post the line below tagging @commonsmade and the handle you're vouching for — that's the whole mechanic. It costs nothing and takes about five seconds.
This opens X's compose box with the text filled in. Nothing is posted until you read it and press send yourself — and you can edit it first. If you'd rather not, closing this changes nothing.