thanks for that information. One other question that im confused. I see i have an address for coinbase and blockchain. So if i have a site send me bitcoin to my blockchain address... dont i always give them the same address? Not sure why ppl say new address or generate new address. Is that necessary? Im confused why can't i use same bitcoin address for my blockchain.
Reusing a Bitcoin address works but it isn't the best idea.
If you give everyone the same Bitcoin address, it can be hard to tell who sent you money and who didn't. When you give everyone a unique address, then you know that any payment to that address is from the person you gave it to.
It is also bad for privacy. With the right tools, anyone can figure out who you are transacting with, how much BTC you have etc
It is always a good idea to use a new address whenever you can.
Which one do you use? Electrum, multibit?
Blockchain.info is a convenient client, but it has some downsides. Recently they had a severe bug that caused people to lose money. The problem is that because it runs in your browser blockchain.info has to be written in Javascript , which is not a good language to write a Bitcoin client in as it is easy to make a mistake with it, and with Bitcoin even a small mistake could cost people a lot of money.
There are other problems too. If one day the blockchain.info website is hacked, the hacker can change the Javascript code and use it to steal your Bitcoins. There are also ways a hacker can intercept the page and change it while in transit (mitm SSL stripping for example), though this is quite difficult (although it is becoming more common).
It is better to use a "real" wallet that runs on your PC.
I would recommend Electrum. Electrum is a very lightweight/quick wallet. Unlike blockchain.info, it is a deterministic wallet, which means you only need to back it up once. It also has a seed that you write down when setting it up, and in the event you forget your password or lose your wallet file you can use this seed to regain access to your Bitcoin. You can also use it to setup "cold storage" if you have a spare PC.
Another good client is of course, Bitcoin Core which is a good client for powerusers. It has lots and lots of features, though it is really resources heavy, it requires nearly 30GB of diskspace and takes a long time to sync. So unless you need lots of features Electrum is probably a better choice.
Multibit is also a pretty good client, though I don't like it as much. I find it is slower than Electrum. It also also not deterministic (IIRC) so you have to back it up regularly. I have also experienced connectivity problems with it a couple of times. It also requires you to install Java runtimes which are pretty bulky, though many people will already have these installed.
Okay if i download electrum and use it, i first have to backup it first? Do i have to backup it everytime i do a transaction or just when i install it? How long does it take to backup it?
So where should i save the backup to? a usb? Dropbox?
So if i lose my computer or have to format computer, then i use that file i saved? So if i don't create a backup with electrum and my computer gets lost or its broken, then i lose all my bitcoins? That was one of the reason i didnt want to use electrum because i heard if computer has problems, u lose all the bitcoin.