This lightweight DAW is bundled with various hardware devices that include it as a starter digital audio workstation for beginners. So, to install Ableton Live Lite on your computer, you would need to purchase a product, like the Arturia KeyLab 49, for example, that includes a Live Lite serial number.
Considering it's called Live they don't have a way to specify that you want to record n number of bars of audio - you have to spend another $800 for push to do that. If you can live with one scene then you can use MSuperlooper. Zenbeats also doesn't support record n number of bars for audio. Both support it for MIDI.