how to erase everything on a macbook 2010
I want to delete everything from my mac book 2.1 (2010) and imac 2011) then reset it to factory mode
MacBook
If these Macs are using hard drives (or a Fusion Drive in the iMac), then you would want to write zeroes to the whole physical drive when erasing the drive. Unfortunately Apple's current instructions assume the computers are either using an SSD (they behave differently when erased), or they are encrypted using Filevault. Apple removed the "secure erase" feature from the Disk Utility GUI interface many years ago which allowed writing zeroes to the drive when performing an erase, so writing zeroes to the entire drive is a bit more difficult these days.
Both these Macs should have access to Internet Recovery Mode (Command + Option + R), but some home Internet connections may not be fast or reliable enough for Internet Recovery Mode. Plus sometimes no matter which keys are used for accessing recovery mode, that the Mac may only boot to the online installer for the OS which originally shipped from the factory...but many times these older online installers have outdated certificates which then require setting the computer's date to an earlier date in 2017 or perhaps earlier.
If these Macs are still able to boot normally or into Safe Mode, then before erasing the drive you should create a bootable macOS USB installer using the instructions in this Apple article (best to use macOS 10.13 as both computers can use it):
Create a bootable installer for macOS - Apple Support
While technically it is possible to write zeroes to the hard drive while using the macOS installer, it involves the command line which is not friendly for people who have never used it before. There is a bootable utility disk which can be used to write zeroes to a hard drive. The older utility is called DBAN, but it can only boot a Mac when burned to a CD and booted from CD. There is a newer utility called ShredOS that will do the same thing, but can be booted from a bootable USB stick instead. You will want to download the 64bit .img version of ShredOS and use the .img file as a source for Etcher (Mac/Windows/Linux) which will create a bootable ShredOS USB stick. Option Boot the Mac by holding down the Option key immediately after hearing the startup chime and selecting the orange icon (most likely labeled "EFI"). Note: the ShredOS USB stick will not be mountable (or recognizable) in macOS since macOS won't recognize the file system used by ShredOS on the USB stick.
After writing zeroes to the whole physical hard drive, then boot into Internet Recovery Mode (Command + Option + R) or from the bootable macOS 10.13 USB installer. Launch Disk Utility to erase the physical drive as GUID partition and MacOS Extended (Journaled). Quit Disk Utility and select "Install macOS".
Of course this all assumes the hard drives are still healthy. If the hard drives are failing, then it may never finish some of these steps or one of these steps may end up with an error.
If the Mac is using an SSD, then just follow the instructions in the Apple article already linked by @FoxFifth since a simple erase of an SSD will destroy all data on the SSD due to how SSDs work.
