Finding collectibles online can be a complicated process for those who are not that familiar with the kind of collectibles in question. Finding collectors comics online, especially for those who are new to it: Where to find them, how the grading system works, and even possible alternatives are each a major problem to those new to the situation and it may help to look at each of these in order to simplify things a little. Just remember that the rarer or more significant a comic is the more expensive it will be and you should be fine; everything past that is just learning how things work.
Finding comics online is not that big of a problem; finding a reputable dealer is. You should start with the auction sites first; these have systems in place that will help you separate the chaff from the wheat quickly and efficiently due to the way that they grade sellers and buyers. Remember to rate them as quickly as possible and you should be good to go, especially if you have had bad service. Also look for the websites of local comic book stores as they tend to feature lots of sales both online and instore, making looking for older comics that much easier.
The grading system is something you need to learn quickly and reasonably absolutely. The system is based on a simple 0 to 10 scale, with 0 being virtually unreadable and 10 being absolute mint condition. For collecting purposes you want a rating of 8 or greater, with the higher the better. Just be advised that the better the quality comic the more expensive it will be, and there are some seriously steep drop offs between grades. Also, keep in mind that there is some debate regarding signatures and how they affect condition, but the general thought is that they increase the overall value of the comic while decreasing the condition.
You may also want to debate your options. In this case we are discussing trade paperbacks and digital copies. While a digital copy is not likely to increase in value, it does allow you to read the comic; for those collecting to read the story or to look at the artwork this may be a great option. Some comics are collected and published with better binding; these are referred to as “trade paperbacks”. While they may have additional features, such as behind-the-scene stories and artwork, they are also cheaper than the collected issues. Keep things in mind while looking for collectible comics online and you should have a really nice collection.