A point, and a time-sensitive one
The Ascendant isn’t a planet at all. It’s the degree of the zodiac coming up over the eastern horizon when and where you were born, and all twelve signs pass that point in a day. It’s the reason Rising needs a birth time. The app only compares it if your time is known, and it leaves it off your profile if it isn’t.
It’s also the start of the whole house system, since the 1st house begins here. Astrologers often treat the planet that rules your Rising sign as carrying extra weight in the chart, which is why you may hear it called the chart ruler.
What it does between two people
An Ascendant contact often explains an immediate reaction. Their Sun on your Ascendant may feel like instant familiarity. Their Venus there can make you feel attractive just by being in the room. Their Mars can bring an awareness of each other that’s physical and a little distracting, and their Saturn can make you feel strangely formal, as if you’ve been asked to sit up straight.
These contacts tend to be strongest early, then fade into the background as you get to know the rest of the person. They count, in the way a first impression counts. They get you to the second date.
When the outside and the inside differ
Someone can have a cool, composed Rising and a Moon that cries at advertisements. If you fell for the composure, the crying may come as a surprise, and if you fell for the softness, you may be baffled by how distant they seem at parties. Neither one is the fake version. Your Ascendant is a real part of you, the part that goes first, usually because at some point it kept you safe.
Your Rising sign page goes into what people tend to assume about you. Asking someone close to you what they thought when you first met, and what changed, is one of the better conversations you can have about this.