BigLuna is gently pointing out that you need to make some progress in Astrology before you start using them.
Their main use these days is in Horary Astrology and that's not something you've ventured into very much. Their use in Natal Astrology is now almost defunct but in the good old days when Astrologers were a power in the world, they were used in every branch of Astrology.
I'm tempted to leave it there but knowing you, you will start roaming the internet for information if I don't say something.
Antiscia is the plural of Antiscion. This is a connection between planets that is similar in effect to a conjunction. Identifying one is not straightforward, without the appropriate software. In effect they are two points in the zodiac which lie equidistant from the axis between the two solstice points (0 Cancer to 0 Capricorn) but lie on opposite sides - like a mirror image.
Thus in terms of Signs, Gemini is the antiscion of Cancer, Taurus is the antiscion of Leo and Aries is the antiscion of Virgo. You can work out the other three sign antscions by following the pattern of moving one sign back in each direction.
The arkward thing is that this also applies to degrees. So the antiscion of 1 degree Cancer is 29 degrees Gemini. and the antiscion of 10 degrees Aries is 20 degrees Virgo (note the two degrees must add to 30). Obviously the same rule applies if minutes and seconds are used as well as degrees.
If you think about it, 0 degrees Cancer is the longest day (a day being the period of light) So Antiscion degrees share the same length of day and night. The closer the degrees are to 0 Capricorn, the shorter will be the length of daylight at the two degrees.
So this is a real connection, not some hypothetical construct. Contact by antiscion is taken as evidence that the answer to the horary question is 'yes'.
Just to pique your appetite there are contra-antiscia, which are points that are mirror images on the equinoctial axis (0 degrees Aries to 0 degrees Libra). These are similar to oppositions. As with antiscia, there is a real link in that signs in contra-antiscion take the same time to rise above the horizon. (equal times of ascending).
In horary a link by contra-antiscion between two significators would suggest that whatever was quesited would not come to pass - the answer is 'No'
Animal, Vegetable or Mineral? John Frawley jokingly refers to them as furry little animals LOL