Your Td-Free should light up in white first, then switch to yellow and finally to purple. The purple means that it has opened a hotspot named, you guessed it, "Td-Free". Connect to it with any device and open http://192.168.71.1 in your browser. Make sure it's http, not https! Once you got that site opened up, insert some filament and you should see the td displayed on your screen!
You can connect your Td-Free to your wifi network so that you don't have to connect to the hotspot manually. To do that, open the website of your Td-Free up and click the small Wi-i config link at the bottom. There, you can enter your wifi credentials. Once you click save, your Td-Free resets. If the LED turns green after startup, it has successfully connected to your wifi, but if it should turn purple, it was unsuccessful and the hotspot is back on. TO access is now over your home network, just find its IP address somewhere in your router.
If you visit http://YOUR_TD_FREES_IP/algorithm, you can change the equation used to calculate the Td value. But only play around with it if you know what you're doing, otherwise you'll be messing up your measurements beyond usable. But if you do so, the default values can always be seeen and set on the page.