There's two different ways to answer a Check-in, from your chat and from the web.
You will be prompted by DailyBot to answer a check-in via chat.
After clicking "Yes, I'm ready" DailyBot will prompt you with your check-in's questions.You can also type "checkins" to answer an specific check-in. There you will be prompted to select the check-in you want to complete.
To answer a check-in from the web you must click on the check-ins button from the sidebar, then select the check-in you want to fill in.
Once you're there click on "Fill out report" and you will be prompted to fill in your check-in!