How do I transfer my stuff from my old smashed iPad to new one

Assuming that the damaged device can be both powered-on and the lock-screen Passcode successfully entered, you potentially have the full range of transfer options available to you. If the iPad will not power-on, your only available option is to restore a pre-existing iCloud or iTunes backup to your new iPad…

These support pages should get you started with setup of your new iPad - and the methods of transferring your data from old to new iPad:

Set up your iPhone, iPad or iPod touch – Apple Support

Transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support

Use Quick Start to transfer data to a new iPhone, iPad or iPod touch – Apple Support

If the donor iPad, from which you are transferring your data precedes iOS12.4, QuickStart will not be available.

“Transfer” is rather a misnomer. In reality, your data and setup is merely cloned to the new device. Nothing is moved or removed from the original device.

An alternative is to restore either an iCloud or iTunes backup to the new device:

How to back up your iPhone, iPad and iPod touch – Apple Support

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

When you are ready, the best procedure for preparing you old device for disposal or reuse can be found here:

What to do before you sell, give away or trade in your iPhone, iPad or iPod touch – Apple Support

How “smashed” is this broken iPad?

Will the iPad power on? Either from battery power or from external power?

Does the touch screen still work?

This broken, smashed iPad still need to basically operate as an iPad to get certain procedures going.

You may, also, need the use of a newer Mac, older Mac or Windows PC to get this data transferred to your new iPad.

If you never made any iPad data backups to Apple iCloud or to a Mac or Windows PC, prior to this iPad being broken and smashed and this iPad does NOT turn on or function, then there is no way to retrieve any of the data inside of this broken, smashed iPad.

This data is, essentially, lost/gone.