This guide shows how to bring up a Raspberry Pi Zero or Zero W without needing to attach a keyboard/mouse/monitor. Basic settings will be configured by editing text files directly on the SD card using an editor on your main PC prior to first boot.
Latest OS tested: Raspbian Buster Lite 2019-06-20
If you need to troubleshoot for any reason, this item is your best friend. For $10, it makes working with a headless Pi Zero so much easier. It's also included with a lot of the kits.
Don't leave home without it.
This is a slightly fancier option specifically made for the Pi. It has the convenience of allowing you to use a standard micro USB cable. It was mainly designed for attaching to male headers, so if you've soldered on something different you'll have to find some way to jumper it.
That's fine but not covered in this guide. Troubleshooting HDMI issues, configuring display settings, and dealing with possible HDMI and/or USB cable and/or power problems are worth a separate guide.