i gave my macbook to my grandson how to i get out of the macbook registration and register him as user

Follow these instructions: What to do before you sell, give away, or trade in your Mac - Apple Support

Create him an admin user,

Sign out of your Apple ID,

He should sign in as his admin user,

He should create for himself an Apple ID and PW; it should already be in his mind when this process starts

Remove your user,

When asked, elect to not keep your Home folder

This will remove you and all your data.

If you wish to keep your data, offload it to an external HDD dead first.

Make a backup immediately.