What the result contains
The result gives the Sun, Moon, and planetary positions by sign and degree. With a known time and location, it also shows the Ascendant, Midheaven, and houses. Choose Whole Sign, Equal House, Porphyry, Placidus, Campanus, Regiomontanus, Koch, or Morinus before calculating; those systems place house boundaries differently, even though the planetary zodiac positions stay the same. Placidus, Campanus, Regiomontanus, and Koch use a clearly labeled Porphyry fallback where their cusps cannot be computed. Morinus projects equal divisions of the celestial equator; its first cusp need not be the Ascendant, and its tenth cusp need not be the Midheaven.
Getting the birth record right
The UTC offset is the civil offset that applied at the birthplace on the birth date. A modern time-zone setting may be wrong for an older record or a daylight-saving date. The birthplace atlas can help identify coordinates and historical offset, but a recorded birth time is still the best starting point.
When the time is unknown
Use the unknown-time checkbox. The tool substitutes 12:00 local time for the planetary lookup and omits the Ascendant, Midheaven, and houses. The Moon can move enough during one day to change its degree, and sometimes its sign, so read a date-only result as an approximation.