The ESP-01 is a great wifi / IoT / Arduino "chewing gum" piece of technology, but programming it is a bit of a technical issue. Fix that with this inexpensive programmer module.
Programming an ESP0-01 (or any other ESP8266 variant) can be a bit of a button-toggling dance even after you get it wired up correctly. This handy little module by Blkbx makes it so much easier, by making it a 1-touch procedure. Plug in your ESP-01, an USB-to-TTL adapter, and use the standard ESP toolchain to do the programming. Just hold the button until the upload procedure starts, and release.
You'll definitely want one of these if you've ever had to breadboard a quicky-programmer adapter for these more than once!