The micro:bit site, which has lots of information on the device's features along with ideas and tutorials, can be found here: https://microbit.org
Most new coders start by using the Scratch-like Makecode editor. It also includes a large number of tutorials that walk you through building the code inside the editor. The block-based editor allows coders to switch between blocks and JavaScript - either to see what their code looks like in JavaScript, or to get more comfortable with coding in it. Below is a YouTube video that walks you through the process of creating some code and getting it onto your micro:bit
Unlike Scratch, the micro:bit code editor doesn't allow you to create an account to save your work. If you use the same machine all the time it will remember some of the more recent programs using cookies. This won't work on the library machines at all, so you or your coders will need to save the downloaded .hex files to a USB stick so that they can be imported at the next session. The video below has a demo of this: