You accelerate for the first half the trip, and decelerate thereafter. If it’s a manned interstellar flight, you’re pretty much limited to a constant G force of not much more than 1 G, but even at that you can approach light speed in less than a year. You just need the propulsion technology for constant 1 G, however you do it.
Assuming you can do it, your biggest problem would be relativistic time dilation. If you make the round trip to the nearest stars at an average speed which is a significant percentage of C, the Earth you return to is quite a bit older than your onboard clock/calendar will indicate.
If you go fast enough and far enough, you might in fact return to a far-in-the-future Earth which saw the end of your civilization in some cataclysm, followed by hundreds of thousands of years of primitive tribes surviving as hunter/gatherers, then more thousands of years as the tribes developed agriculture and trade routes and metal-working, then more centuries in which technology advanced to roughly the equivalent of what we had in 1947.
In the possibly millions of years since your departure from Earth, your species has undergone radical physical transformation to the point that the only commonality remaining is the basic form of torso, head and two arm and two legs.
Your return to your home planet would be interpreted as the arrival of aliens. No doubt about it.
Time dialation actually works the other way around. If you are on a ship moving at .9c and going to a system 10 light years away and back, from the outside it will look like the round trip takes 18 years. From the inside of the ship it will take a lot less. (Sorry, too lazy to do the math on a Saturday.)