I get that time passes slower for those outwith the ship, but I'm struggling to wrap my head around how long it would take those on the ship to travel large dis

I get that time passes slower for those outwith the ship, but I'm struggling to wrap my head around how long it would take those on the ship to travel large distances at close to light speed - whenever I think on this topic, my head almost bursts with awe and wonder! Let's consider a ship, travelling from Earth, and say it somehow accelerates almost instantly to just below light speed, and travels for a distance of 1 light year. How much time would pass for those still on Earth, and for those on the ship?