When Jupiter, the planet of growth and excess, sits exactly opposite your natal Ascendant in the sky, it lands on your Descendant, the point that rules one-to-one relationships and how you meet other people. A transit is a planet in today's sky making an aspect to a point in your birth chart, and an opposition places two points 180 degrees apart, pulling in both directions at once. For this transit, one end is you as the world sees you, and the other is what you want from, and offer to, the people closest to you. Jupiter does its work from the relationship side of that axis.
Because Jupiter takes about 12 years to circle the whole zodiac, this aspect comes back roughly once every 12 years. Jupiter also turns retrograde every year, so it often crosses the exact point three times in a row, meaning the transit can stretch across a few weeks or run to a few months rather than passing in a single day.
One thing to know upfront: your Ascendant depends on your birth time. If your birth time is off by more than a few minutes, the degree of your Ascendant shifts, and the timing of this transit shifts with it. An accurate birth time is worth tracking down before you read too much into the dates.