If i buy a phone of a friend and they have connected to the clud, can i put my account in and use the phone or will it lock me out?

Before you purchase the device, make sure your friend follows these instructions:

What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support

Once you are ready to purchase, check to make sure the Activation Lock has correctly been removed by going to the link below, or following the instructions provided:

You can check the current Activation Lock status of a device by visiting icloud.com/activationlock from any Mac or PC.

Or you can follow the steps below to make sure that you can use the device you purchase:

1. Turn the device on and slide to unlock.
2. If the passcode lock screen or the Home screen appears, the device hasn't been erased. Ask the seller to completely erase the device by going to Settings > General > Reset > Erase All Content and Settings. Don't take ownership of any used iPhone, iPad, or iPod touch until it's been erased.
3. Begin the device setup process.
4. After choosing a language, choosing a country, and connecting to a network, the device will begin activation. If you're asked for the previous owner’s Apple ID and password, the device is still linked to their account. Hand the device back to the seller and ask them to enter their password. If the previous owner isn't present, they can remove the device from their account by signing in to icloud.com/find. Don't take ownership of any used iPhone, iPad, or iPod touch until it has been removed from the previous owner’s account.

You will know that a device is ready for you to use when you're asked to “Set up your iPhone," “Set up your iPad," or “Set up your iPod” during the device setup process.

Cheers,

GB