I backed up my lap book onto a hard drive. How do I bring things into my new iMac desktop?

If you used Time Machine to backup your stuff to the external drive, then you can use that external drive at the time that you setup your new Mac. The Setup Assistant will ask if you're transferring files and data from another Mac or Time Machine backup.

If you have already setup your new Mac, then you can use Migration Assistant (in Applications folder) to migrate your files back from the TM backup.

Restore your Mac from a backup - Apple Support

Move your content to a new Mac - Apple Support

You can backup your Mac with Time Machine. To bring your things, you have to back it up first.