If you'd like to have a pet but don't have a lot of spare time, consider getting a pet fish as opposed to a dog or cat. Fish are beautiful and interesting, they don't cost too much, and fish care is much less stressful than training a puppy or teaching a kitten to use a litter box.
The first thing you need to decide is what kind of aquarium to buy. Size and shape are important considerations, because your fish tank requires a good location. It needs a stable flat surface, preferably away from doors and windows to minimize temperature changes. At the same time, you'll want to pick a place that's easily seen - an aquarium full of tropical fish is a great conversation piece and almost a work of art. I recommend a ten or twenty gallon tank because that's large enough to host an interesting community of fish but not so expensive or hard to care for as to be intimidating.
Once you've picked their home, you can select your fish. For a first aquarium, select fish that are fairly easy to care for. There are a few fish, like betas and goldfish, that can just live in a bowl full of water, but most tropical fish require at minimum, a pump, a filter and light. You can often buy an aquarium "starter kit" that includes all of these things. With a basic aerated fish tank, you can select from a wide variety of easy to care for tropical fish.
Some excellent choices include danios, mollies,
platys and tetras of all kinds. These fish all have peaceful temperaments and similar sizes, which means they can coexist without anyone getting eaten. They are easy to care for and they come in a number of attractive colors and patterns. Buy danios and tetras in schools of around five, and platys and mollies in singles or pairs. If you want to buy a male, which are larger, flashier and sometimes have fancy fins, only get one. Platys and mollies are similar enough that the males may fight each other. With tetras and danios sex is less important, which is fortunate because it's also less obvious.
When you go to the fish store to pick your pet fish, there are a number of temptations you will need to resist. Do not buy more fish than you think you can handle. An often quoted rule is "one inch of fish per gallon of water", but that represents a maximum. I recommend about seven fish from the list above for a ten gallon fish tank.
Remember, do not buy fish that are too large for your aquarium. The fishes described in this article average 1-2 inches in length, which makes them suitable for small tanks. Avoid any fish that are described as "delicate" (like angelfish) or "aggressive" (like Oscars). And don't even think about a salt water tank if you're just starting out. If you select a suitable number of easy care fish and a simple aquarium setup, your first experience with owning fish will be both relaxing and rewarding.