How the calendar differs from transits on a date
The transit page shows a snapshot: which aspects are to the natal chart on a specific day. The calendar answers a different question: when an aspect will become exact. Instead of a list of orbs you get a list of dates, each of which has a transiting planet, an aspect, and the natal planet it applies to.
How dates are calculated
Positions of transiting planets are calculated for each day of the period, and when the orb of an aspect changes sign, the moment of the exact aspect is refined by dividing the interval. Therefore the date in the list is not the day when the aspect is “approximately present”, but the day on which it reaches the point of exactness. The Swiss Ephemeris calculation is performed in your browser.
Why the Moon is not in the list
The Moon moves 13 degrees per day and with a daily step its aspects cannot be captured: between two consecutive days it manages to form and break an aspect. Lunar transits make sense with an hourly step, and there is a separate tool for them - the lunar calendar.
How to read the list
Transits of slow planets carry more weight than fast ones: a Saturn aspect lasts months, a Mercury aspect a day. The ℞ mark next to a planet indicates that the aspect is formed in retrograde motion, and therefore will repeat: a retrograde planet passes the same degree three times.