Drag blocks or write MicroPython, then flash it straight to the board over USB - no install, nothing to download.
Plug the micro:bit into this computer with a data USB cable (some charge-only cables will not work).
Press Flash. Chrome asks which device to use - pick "BBC micro:bit CMSIS-DAP".
If Chrome says no compatible devices were found, the board needs a firmware update: hold RESET while plugging in, drop the firmware hex from microbit.org onto the MAINTENANCE drive, then try again. Until then, Download .hex and drag it onto the MICROBIT drive.