The furthest distance humans have travelled from Earth is around 380 000 km — the Moon. This happened several times in the 1960s and early 1970s.

The furthest distance any manmade object has travelled from Earth is around 140 AU — 140 times the Earth-Sun distance. This object is Voyager 1 and is an interstellar probe launched in 1977 by NASA to study the outer solar system and beyond. Currently, it takes radio signals around 19 hours to reach Voyager 1 from Earth!

Now, the furthest possible distance we can travel is really an open question. It of course depends how fast you travel and for how long but one thing is for certain: space is unimaginably vast. The nearest star to Earth that isn't the Sun is Proxima Centauri and Voyager 1 would need to travel for another 40000 years to reach it.