Time travel is both incredibly simple and very complex. The simple part is to merely look up. This is easiest at night when the sun isn't out, but believe it or not, with proper planning (and precautions) you can sometimes see other planets and even stars and satellites during the day! Since light can only travel at the speed of light (approximately 300,000 kilometers per second; 186,000 miles per second; 671 million miles per hour) the light that you see from something far way may have taken a long time to reach your eyes. Light coming from the moon shows us the surface of the moon as it was about 1.28 seconds ago. That’s how long it takes a photon from the sun to bounce off the moon and hit our eyes. But that photon from the Sun took more than eight minutes to travel from the Sun to the Moon in the first place, so when we look at the Sun or the Moon, or anything else in the sky, we are peering into the past. In essence, we become Time Travelers!
It's also easy to look even deeper into the past. While there are lots of objects that you can see with your naked eyes, a pair of binoculars will let you see many, many more. They are also brighter and bigger in binoculars than they are with just your eyes. Turn towards M31 (the Andromeda Galaxy), and you’ve just time traveled 2,500,000 years into the past. That's how long it takes light from the stars of M31 to reach Earth.
Of course, an Astropotamus wants to be able to look very deep into the past and be able to photograph it, which requires something more complex than binoculars. It takes a Time Machine. Time Machines look just like telescopes, which operate by gathering, bending, and folding light so that light that travels a long way can be made brighter and bigger than just what the eye sees. By gathering all this extra light and focusing it onto a small area, the image at that point gets very bright with lots of detail. Sort of like having a 100 megapixel camera instead of a 10 megapixel one. The Time Machine then bends the light again so to spread this focused light out, making it bigger. This is similar to why a 100MP image can be zoomed in or blown up much more than a 10MP image can - there’s more information in the source, so you can magnify smaller portions of it more easily and still have it look good.
The end result is a lot of magnification and a (usually) bright image so that a camera can be put at the end and an image captured. With proper exposure, a little luck, some practice, and some post-processing on the computer, the camera can take long exposures that gather even very faint light that your eye can’t see. This lets the camera capture images from very far away or from very dim objects, which lets an Astropotamus share their time travels with the rest of the world by posting the images online!