LCD screen displays lines on my 2017 MacBook Pro 13 in.

As a work-around when the built-in screen does not light up due to probelms in the display itself, Your MacBook Pro 2017 model can support up to TWO external displays. Your TV set could also be pressed into service as a display.

USB-C Digital AV Multiport Adapter - Apple

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Who told you the screen was cracked?

If that is an accurate assessment, then it means you need to have the computer repaired if you want to keep using it.

You can make a Genius Bar appointment for hardware/software service and support using this link: Contact Apple Support - Apple Support

Get your Mac repaired and see how much will it cost: Mac Repair & Service - Apple Support 

Call Customer Support (800) MY–APPLE (800–692–7753) or on line /getsupport.apple.com/ 

or call AppleCare Support at 1-800-APLCARE (800-275-2273) 

The best way to transfer all your files will be to use an external drive and Time Machine to back up your stuff to that.

When you buy your new Mac make sure to get one with equal or greater storage. That way you can transfer your files from the backup drive to the new Mac when you set it up for the first time.

micki223 wrote:

So, when I get the new laptop, the tech will be able to do the external drive and Time Machine for the transfer, even though I can’t get into the laptop?

You are not asking Apple employees here but other end users. We cannot give you an official answer regarding what Apple can/will do in-store for set-up help. Contact the store you plan to use to see if they can do set-up assists.