Of all the hobbies you could get into, none offer the unique experience that comic books do. It's a medium unlike anything else, a marriage of words and pictures. And they're not just the domain of kids anymore. In fact, kids don't really read comics as much as they used to – they're occupied with video games or computer games, by and large. But despite the changing and somewhat aging readership, if your child isn't much of a reader and that concerns you, consider introducing them to comic books as a way of easing them into reading more.
There are many places where you can buy comic books. A few decades ago, it was more common to find them at newsstands and convenience stores. You can still find them there, but most people shop for comic books at a comic book store or a bookstore. It depends on what you prefer to collect, really. If you like single issues, you're likely headed to a comic store; if you prefer graphic novels or trade paperback collections (known simply as "trades" in comic lingo), you're going to a bookstore.
Both stores will carry these items; the difference is that a comic store will have a much larger selection of singles and trade paperbacks, while a bookstore will primarily stock trades and may have some single issues on a spinner rack. Many people are collecting trades these days, so bookstores have a larger selection of graphic novels than ever before.
One misconception about comic books is this: if a comic book is old, it's worth big money. Sure, it can be worth something, but age alone doesn't mean that the book will automatically be worth a fortune. There are two factors here that determine a comic book's value: scarcity and popularity. Scarcity is easier to come by in old comic books, but main factor here is popularity. Say you have a comic from the '50s about John Wayne or some obscure cartoon no one remembers anymore. That book won't go for as much as a Justice League of America comic from the same era. Demand plays a large role in determining value.
On the other hand, some old comic books really are worth a fortune. This often happens with major events in the comic's history, like the first appearance of a character. For example, the first appearance of Superman (Action Comics #1, June 1938) is currently valued at $675,000 in near-mint condition. Rumor has it that only three near-mint copies of that 70-year-old book exist in the world.
The Internet has changed the way people buy, sell and read their comic books. There are various online retailers now, such as Mile High Comics and Graham Crackers Comics, and there is of course, eBay. EBay is a good place to find those obscure books you can't find anywhere else, but it may not always be the best bang for your buck. Watch out for inflated shipping prices and try to buy from reputable sellers with a good rating.
Online comic books also take the form of webcomics. There are many creators out there publishing their work online, such as Warren Ellis' Freakangels, Scott Kurtz's PvP and Nicholas Gurewitch's The Perry Bible Fellowship. Marvel Comics recently began soliciting digital comics through their website. With the purchase of either a monthly subscription rate or an annual rate, you can browse their archives, spanning 45 years of comic book publishing.