How do I get to TD Garden from Grafton T Stop and how long willm it btake

Take the Orange Line to Back Bay, and take the Framingham/Worcester Line train. It'll take 1 hour 37 minutes.

Comuter rail to back bay and orange line to NS

But once you get to South Station, take the red line one stop to Downtown Crossing, then take the orange line to North Station. TD Garden should be above the station