I've read the rule book, got the cheat sheet and watched some people play online, but while Marvel Heroic Roleplay seems easy enough, I still don't feel like I "get it". Where is a good place to play or learn, particularly online? I've looked on roll20.net but didn't find the game listed (supposedly because it isn't grid based).
There are several VOIP games running. Some are actively recruiting on the Margaret Weiss Productions forums (http://www.margaretweis.com/forum/index.php), and on RPG Geek (http://rpggeek.com), as well as the GooglePlus MHR community (https://plus.google.com/communities/113114436417291762579).
In the case of RPG Geek, the people I've seen looking for players are posting in geeklists, especially the 2014 RPG Challenge: Play 5 Games New to You list.
Also, since MHR is Cortex Plus, much of the mechanics are shared with Leverage, Smallville, Firefly, and Dragon Brigade. Looking at those can shed light on the fuzzier areas of MHR.
Further still, Cam Banks, the designer, is active in the G+, RPG Geek, and MWP forums, and often helps people grasp it. He's VERY accessible online, and seems to be a genuinely nice guy. He's proud of MHR. Just don't ask about why it was cancelled.
You might want to check out the communities on Google Plus. For awhile I know one of my friends ran "Marvel Mondays" - he'd run an online hangout (video chat) session for about 2 hours every Monday with a good focus on drop in games. The nice thing is that G+ Hangouts has solid dice roller options. Start asking around and I bet you'd be able to find someone willing to run a game or play in one.
My answer is largely copied from a D&D specific answer here: I have read the D&D PHB but am still having trouble grasping some of the basics, how can I learn more? because I am reading between the lines and assuming some of this is that you're new to RPGs in general, not just Marvel, right?
When you're just getting started, it is certainly possible to figure out the game from the books and just start running it for your friends. That's how I and others learned to game "back in the day." But there are certainly things that can help.
Huh? If you are profoundly and existentially confused about "what is roleplaying", see What is role-playing, and where do I start? and if confused about the general nature of D&D see I'm at a loss with “Dungeons and Dragons.” How does one play it, anyway? - you're not asking about D&D but that question is really fairly generic.
Read the Rulebook. Cover to cover. I know you said you've read it, but no really, read it. Modern RPGs are pretty "legalistic" about using terms that mean a specific thing and don't change over time. If you closely engage and read the book, many of those questions will go away (and you'll get less newbie haters when you subsequently go looking for help). Use normal lookups - a word you don't understand? If it's a game term look at the Glossary or index; if it's a normal English word check a dictionary.
Join a game. This is going to be your #1 route to very, very quickly answering 200 possible basic questions because in one round of combat you'll see people doing all the dice addition, checks, etc. Check with your friends. See Where can I find other RPG players? Demos and games are being run in most gaming stores and conventions on an ongoing basis. You can join in, or if you just want to watch, you can watch. There's meetups, conventions, any number of places where you can join or observe a real live game.
Watch a game. If you are having trouble in meatspace, consider watching one of the many video and/or audio podcasts of what is usually called "actual play." See Where can I find actual play podcasts for RPGs?, search on iTunes, etc. Or you can read play-by-post games, see Where can I find transcripts of actual game sessions?
Seek help. Needless to say if you know anyone who's played an RPG/that RPG they can explain it to you better (and I GUARAN-DAMN-TEE you know someone who's played at least D&D - it's been around since the '70's and have been popular over time, so a parent, a teacher, a friend, someone's done it - ask around). If you are a brain in a jar, then for super basic "I totally don't know how to do this" questions it's probably quickest to do it in RPG.SE chat. If you want someone to personally take you under their wing and show you the ropes, ask for help there or on a forum for that game.
Ask questions on RPG.SE. But try these other things first. It's not that beginner questions aren't welcome here - there are just some questions so basic that it's much more efficient to have someone in person or chat talk you through "how to add 1d8 + 4" without clogging the site with hundreds of those questions - you'll get answers faster. As soon as you have played a game, further questions can be asked here.