Enter your time by day - basically the day slice of the weekly timesheet.
By default, it shows the information for today, but you could also select another date or move from one day to another via the < and > buttons.
The Day Only toggle switches between all entries in the week (including the ones without hours) or just the entries with time for that day. Day Only can set by default in Custom Settings and is convenient, if there are many time entries in a week.
The timecard optionally allows you to check in in the beginning of your day and check out at the end. It calculates the number of hours and shows the delta between the entered hours (see yellow arrows).
The lines displayed are part of the time entered for the week, just showing the hours for that day.
The information displayed is the same as on the weekly timesheet - including custom fields and the type of project selection (Individual, dynamic, dropdown).
Configure the Description options e.g. by using only daily/weekly descriptions (up to 255 characters) or a long description.