Can jailbreaking ruin your iPhone 4?

I want to jailbreak my phone but i'm really nervous that it will erase all of my data and my aps and songs.
When you jailbreak, can you still download App Store apps?
How long does it take on average?
Is it worth it? What can you do?

I have an iPhone 4 and I'm jailbroken and it's pretty awesome! I'm sorry for this really long answer haha. Jailbreaking is pretty easy and you can look up a "How To" video on YouTube. When you jailbreak your device you get an app called Cydia. This app lets you download many things such as apps, themes and tweaks for your phone. Jailbreaking is pretty safe and no it won't ruin your phone(but it does void the apple warranty, which means apple won't help you if you break your phone, but if you've had your phone for over a year the warranty has expired so it is safe to Jailbreak) or delete any of your stuff and you will be able to access the App Store. Now if you do jailbreak you're going too need to know a few things about your phone: What phone it is (which is the iPhone 4) and what iOS you have which you can see in your settings>general and scroll down till you see Version. So now go on YouTube and look up "How to jailbreak iPhone 4 on iOS__". I suggest you jailbreak with either redsn0w software or evasi0n software. They're the best software to jailbreak with. Now once you are jailbroken you can look up "Awesome tweaks for iPhone 4" on YouTube so you can see what cydia has to offer. Here are some of my favorite tweaks I suggest you look up:

Movie Box (free movies and TV shows)
Music Box (free music)
iStreamNet (Free TV shows)
Bridge
Barrel
NC Settings
Custom NC Background
Zeppelin
Springtomize 2
Activator
Color Keyboard
Icon Renamer
Winterboard
Password Pilot
Auxo
vShare (free AppStore apps )

And that are just some of the tweaks I suggest there are lots more out there.
Now some tweaks cost money but there are ways you can get them for free.look up on YouTube "how to get cydia tweaks for free "

Well that's about it I know this is long and can seem like a lot of info to take in haha but it's pretty easy if you're still confused look up on YouTube "how to use cydia"

Anyways back to the point Jailbreaking is easy, safe and fun and I don't have a boring phone anymore, no longer do I have to pay for music, apps and new movies. Hope I helped and have fun with your new phone.