How do I back up my Apple laptop and iPad to iCloud

To backup the iPad, see instructions in How to back up your iPhone, iPad, and iPod touch with iCloud - Apple Support

Apple offers iCloud Backup for iPhones and iPads but not for Mac computers.

A backup does not free up space on a device. It creates a second copy of the information on the device and saves it somewhere other than on the device so that you can recover in the event of a problem.

You can potentially free up some space on a Mac by using the Optimize Photos option of iCloud Photos and the Optimize Mac Storage option of iCloud Drive. See below for more information.

It is possible to sync data from a Mac to iCloud if you turn on those options (e.g., iCloud Photos, iCloud Drive including the Desktop & Documents option). Syncing has some of the benefits of a backup (and the benefit of being offsite) but is not the same as a backup. Major differences include the fact that not everything on your Mac can be synced and the fact that if you delete something, accidentally or otherwise, there is only a limited time period (30 days in most cases) during which it can be recovered.

Also see: https://support.apple.com/mac-backup

And more information on syncing in:

Set up and use iCloud Photos - Apple Support

and

Access and manage files in your iCloud Drive - Apple Support

and

Add your Desktop and Documents files to iCloud Drive - Apple Support

I'm not sure I understand your question. Be aware that any file that you delete on your Mac will also be deleted from iCloud (assuming that they were synced to iCloud).

But other than that, I don't know how I could give any advice about deleting files on your Mac as I have no idea what you have on it and what you want to keep. However there may be something in the following that will help: Free up storage space on your Mac - Apple Support My first thought from that link would be to: "Move files to an external storage device".

The following may help: Locate backups of your iPhone, iPad, and iPod touch - Apple Support