Marvel’s Official Site is a good example of a source from where you can read comics online, for free, and legally. The company charges you for monthly subscription fees before you can gain access to tons of titles. You can instead opt for paying for individual issues. However, it also offers access to its free collection which you can read even without subscribing or even registering. There are at least 50 free issues made available at the moment. Not too many indeed, but it should be enough when you currently cannot afford any at all to begin with.
DC Kids and Read DC are two offerings from Marvel’s longtime rival. The company might have kept up with its rival just recently but in terms of comic book material, DC has never been one to back down and time and time again made Marvel run for their money. DC Kids is, as you guessed, dedicated to DC-living kids out there. Read DC, on the other hand, is specifically aimed for the adults. The system with Marvel goes the same for this; you pay for issues or get some for free. Either way, you need to set up an account on the website for access. Alternatively, you can just use your comiXology account (if you have one) instead to gain access the website’s entire database.
Dark Horse Free Pages is what it is, a collection of free comics from the publishers for people to read legally. As one of the big names in the industry, Dark Horse follows suit with their own version of free offering of some of the latest issues. Titles such as Elf Quest and Overwatch can be accessed through this website. The free collection offered here is not at all large but they are nonetheless worth a peek.