How will humans travel to different galaxies?
It is quite unlikely that humans will travel to other galaxies.
Galaxies other than our Milky Way and is smaller satellite galaxies are millions of light years away. Given that nothing can travel faster than light any such journey would take millions of years.
Even is such a journey was undertaken, the ship would have to be completely self sustaining. Intergalactic space is almost empty.
The only option is new physics. A wormhole connecting two remote points in space is theoretically possible. We just don't know how to make one.
Also, our theories of relativity and quantum mechanics each explain and predict things with high accuracy. The two theories however are incompatible with each other. We know that new physics is required to unify these theories and to explain black holes.
New physics may provide a way of travelling millions of light years in a reasonable time. So, with our current understanding travelling to another galaxy is not feasible. Time will tell.