Your processes run in the background until closed with task manager or another program like advanced task killer.
For example, you're reading your book and you want to check a website. Just hit the homescreen or open your apps list and choose your browser, go about your business, then all you have to do is just open back up the kindle reader and everything is just as it was left.
If you get a text while reading, use the drag down menu at the top view the text, respond, etc. then you can use the back key until it takes you back to the kindle app as well.
Your phone stores that info in ram until you end the program with a task manager or turn off / restart your phone.
I came from a Pre too, this phone absolutely blows the Pre out of the water.
Task killers are a touchy subject

Everyone has opinions on if they work well or not, it comes down to how you want to control your device and knowing what programs and services you can actually kill off without ill effecting your phone.
After coming from the Evo I've opted not to use a task killer as most Froyo devices running JIT and what not are much better at managing memory and what not by themselves without a user input. Some people have to have absolute control over their device though

Android is very good at multitasking though, as you can hold down your home button on the epic and it opens a pop up with your most recent apps and an option to go to a "task manager" where you can kill off apps running

so it has a built in one that works just fine for me.
I rarely kill anything though because android is really good at deciding if it needs to close it or just cache it. depending on how much memory and what not your phone has available and if it needs more to complete your current task

I say jump ship!! Immediately

Titanic has struck the iceberg get on a life boat while you can

You will not regret the switch from the Pre. I had the Pre on launch day and used it for awhile until I got tired of the crappy build and jumped ship to a BB Tour so I could BBM my wife

Then I got bored

<not hard to do> lol. So I jumped ship to an Evo and loved Android and can't go to any other OS

But I couldnt deal with the Evos battery life it was absolutely horrid!
So I found a Pre on craigslist and had it for about 2 days before I couldnt take not being on Android having the widgets and apps available that arent available on the Pre...and the Pre seemed horribly slow after coming from the Evo lol.
So I went into a sprint store and fell in love with the Epics screen!!
And it has a keyboard which to me is essential and will be the first question I ask about a new device before I switch lol
Have to have it

Like a condom (or a gun) I'd rather have it and not need it then need it and not have it

So I've had the Epic for a few months and rooted it after about a week and absolutely love the options available. Some custom ROMs out there are unbelievably fast compared to stock and the Theme options are such a great way to customize your device and keep it "fresh" so you dont want to swap out to a new phone if your a phone whore like myself lol
I have a feeling I will be keeping this phone for quite awhile...until a nother physical keyboard slider comes out that outshines my Epic
...wow...I totally misread your post hahaha...you've already switched doh! Too much coffee and forum viewing can be dangerous
Summary: Just hold down your home button and it will bring up your recent apps you've been using. When you back out of a program Android puts it into a cache to kind of store where and what you were doing. So if you want to bounce out of an app just press the home button go to your new app play around and then either press home again and go about it that way or hold it down and you can swap to it that way
Sorry for the long winded post lol thought you were contemplating on switching lol didnt realize you switched already haha