The micro:bit extension for scratch allows you to connect wirelessly with the micro:bit. There are a couple of steps to set this up and then you can use the blocks in all sorts of programs.
1. Install Scratch Link
2. Flash the micro:bit over USB with the Scratch .Hex File, you will see the five character name of the micro:bit scroll across the screen eg 'zutiz'.
3. Connect to the micro:bit in the Scratch editor
Here's a demonstration of how to do this
Once you're set up, ou can then try out these Scratch cards for micro:bit
Other ways to interact with Scratch and micro:bit
Scratch to micro:bit bridge
You can use the scratch to micro:bit bridge, developed by MrYslab:
You can use the S2Bot App plug-in with Scratch, which allows any compatible BLE controller to interact directly with Scratch project: