I have an Iphone given to me (used) first it has a passcode and I want it unlocked. Should I get the passcode first

try this..
Unlock Disabled iPhone/iPad/iPod without iTunes through Find My iPhone

1. Go to icloud.com/#find from another device or computer.
2. If prompted, sign in with iCloud Apple ID.
3. Click All Devices at the top browse window.
4. Select device which you want to erase.

More items...

Forgot iPhone Passcode - How to Unlock Disabled/Locked iPhone or ...

How to disable iPhone to unlock it Google Search

You can't unless you do a factory reset, this wipes the phones memory clean along with the password or code.

You can simply follow the steps below:

1. Connect iPhone to computer.
2. Select iPhone in iTunes "Devices" and click "Summary".
3. Click "Check for Update" to see whether there is a new version for iPhone software.
4. Click "Restore" and follow the instructions to complete the restore process.
5. Choose "Restore from iTunes backup" when iOS Setup Assistant asks to set up your iPhone.

Or refer to the source page: Forgot iPhone Screen Lock Passcode How to Recover Lost Data on iPhone...

To recover a locked iPhone iOS Forgotten passcode or device disabled after entering wrong passcode

iPhone must be recovered on a PC or Mac to solve this problem.

CLICK HERE

It depends on the severity and the settings you have given the iPod... Here's the full explanation. I would recommend reading the second paragraph first, but the solution if you really forgot your password is in the first paragraph.
If you cannot remember the passcode, you will need to restore your device on the computer that was used to originally sync the iPhone or iPod touch so that you can reset your passcode and resync the data from the device (or restore from a backup). If you restore on a different computer that was never synced to the iPhone or iPod touch, you will be able to unlock the device for use and remove the passcode but your data will not be present. Refer to "Updating and restoring iPhone and iPod touch software."

"If you enter the wrong passcode too many times, you'll see a message that says "iPhone is disabled" and to try again later. If you repeatedly enter the wrong passcode, iPhone or iPod touch will be disabled for longer intervals, before you can try again. After too many unsuccessful attempts, you won't be able to try again until you connect to the computer you normally sync with. Note that starting with iPhone 2.1 software, there is a setting to cause the device to erase itself after 10 consecutive incorrect password attempts. This setting is off by default. It  can be turned on by tapping Settings > General > Passcode Lock after you enter a correct passcode."
The full article can be found here: http://support.apple.com/kb/HT1212

It depends on the severity and the settings you have given the iPhone and whether you have the computer that you synced your iPhone with... Here's the full explanation. I would recommend reading the second paragraph first, but the solution if you really forgot your password is in the first paragraph. 
==If you have the computer you synced your iPhone with==
If you cannot remember the passcode, you will need to restore your device on the computer that was used to originally sync the iPhone or iPod touch so that you can reset your passcode and resync the data from the device (or restore from a backup). If you restore on a different computer that was never synced to the iPhone or iPod touch, you will be able to unlock the device for use and remove the passcode but your data will not be present. Refer to "Updating and restoring iPhone and iPod touch software."

"If you enter the wrong passcode too many times, you'll see a message that says "iPhone is disabled" and to try again later. If you repeatedly enter the wrong passcode, iPhone or iPod touch will be disabled for longer intervals, before you can try again. After too many unsuccessful attempts, you won't be able to try again until you connect to the computer you normally sync with. Note that starting with iPhone 2.1 software, there is a setting to cause the device to erase itself after 10 consecutive incorrect password attempts. This setting is off by default. It  can be turned on by tapping Settings > General > Passcode Lock after you enter a correct passcode." 
The full article can be found here: http://support.apple.com/kb/HT1212
==If you don't have the computer you synced your iPhone with==
If you don't have the original computer the iPhone synced with, the only solution is to force your iPod Touch into recovery mode and then restore it. You will lost all the data on the iPod Touch, but after this method is done, everything will work. You can find the steps to solving this problem here: 
http://support.apple.com/kb/HT1808?viewlocale=en_US

how can i reset my ipod touch when its disabled