Invitations to respond online to the Census will be sent out between March 12 and March 20, 2020. The invitation will look something like this:
After a few weeks, if you have not responded online, you will receive a paper questionnaire. If you have not responded by May 13, 2020, then a Census taker may visit you in-person to collect the data.
Statistics from previous Censuses is available online at data.Census.gov.
The web site is includes more than just decennial (every 10 years) Census data. The American Community Survey is administered every year, and estimates based on this survey are also available. (The American Community Survey asks many more specific questions, and provides a greater variety of information.)