As someone who is comparatively new to ArM (having started 3-4 years ago) and with an extensive background in D&D i feel like I am quite qualified to help you out. In addition I am a very seasoned GM, with extensive practise in introducing new players to various TTRPGs.
I will start by saying that in a weird way Ars magica has both a lot in common with D&D and also very little in common with D&D. I know it sounds weird, but its true.
First off, the commonalities.
In Ars magica the fundamental mechanic of the game is that you resolve actions by rolling:
a die + a bonus related to the inherent capabilities of your character + a bonus derived from the skills that your character has acquired through practise.
In D&D these numbers are called "attributes" (for the inherent bonuses) and "skills" (for the ones you acquire through practise)
In ars magica these are called "characteristics" (for the inherent bonuses) and "abilities" (for the ones you acquire through practise).
Though in Ars magica proficiency in combat is treated like an ability, rather than having its own mechanic for improvement.
This is mainly where the similarities end, and you might be tempted to say, that this is only one similarity and its relates purely to meta-mechanics, and you would be right to say so. But IMO this is actually a huge similarity, because it means that your group wont have to learn a whole new way of resolving actions. Instead they can start to learn the game by making comparisons like "okay Charisma is split up into Presence and Communication" or "Deceive is called Guile in this game".
For the differences, the main one is that Ars magica is entirely dissimilar to D&D in its scope. D&D is mostly about a group of homeless heroes (or murder-hobos if you prefer) who roam around doing heroic deeds, mostly involving killing various things, creatures and humanoids. This means that while D&D officially rests on 3 narrative pillars (combat, social interaction and exploration) in practise one pillar, namely combat usually takes preference, with the other two playing second fiddle. D&D games are usually fast paced, with rapid changes in location and cast of NPC's.
Ars magica is about a group of wizards who live in the same place, and who really need that same place to be a stable environment where there is as little excitement as possible. They have to develop stable working relationships with the neighbors (both magical and normal (mundane if you prefer)).
Because of the way Ars magica is designed, the game doesnt work for fast paced D&D-esque games. The game really shines when you have time to develop relations with the same NPC's over time, and to get to know the local area. This is a game that literally and unironically rewards players for getting the interior decoration on their room just right.
By way of example. Imagine a story that starts out with a dragon that plagues a local village.
In D&D this game is about how the heroes show up in town, figure out where the dragons lair is, then the lair is a big dungeon with lots of minions that the heroes kill, one group after another, then they kill the dragon and take its (literal) pile of treasure.
In ArM this game is about finding out why there is a conflict between dragon and villagers and finding a way to, ideally, resolve it peacefully. It is of course a possibility to kill the dragon, but in ArM dragons rarely have large piles of loot to sleep on. Dragons also generate magical power where they live, and wizards need this type of power to grow their own power, so killing the dragon might actually have adverse effects on the magical powers of the wizards. This means that you have to negotiate and find a way for the villagers and the dragon to sort out their differences. Also if you chose to fight the dragon, you are in real risk not just of dying, but of being injured. In D&D injuries are mostly gone the next day. In ars magica being injured takes a long time to recover from, and you get less XP when you are recovering (!).
Thus the primary goal when trying to pitch Ars magica to your group is to try to figure out if your group is even interested in such a game. I know roleplayers who like the fast paced combat-first nature of D&D and thus would hate to play Ars magica, if your group is like that, then you are out of luck.
In terms of actually getting started, I would recommend that you sit down, maybe with a friend/family member and make some characters, just to get the hang of it. Take frequent breaks if you need them. The character creation system is really the weakest part of this game (IMO), not because you are limited with what you can do with it, but rather because there are practically no limits to what you can do with it, and the game makes almost no attempt at trying to hold you hand while presenting this near limitless amount of options to you.
Also the game is very weak in terms of actual content published. There are almost no scenarios published, very few fully fleshed out covenants, characters, magic items, vis sources, books, libraries, etc.
It has a very diverse selection of rules and subsystems to play with though. I would recommend you stay away from them until you are quite comfortable with the main system. There is no reason to overwhelm yourself further with rules for mysteries or how to simulate the life of a craftsman in detail (yes that exists). I count covenants in this section too, but it is a good place to start out once you feel ready to move on from the core book.
My best pitch for ars magica is this:
Imagine you are a bunch of professors at a university department. You have to figure out who applies for funding, who collects research samples, who teaches the students, who is responsible for dealing with uni-management and who is responsible for the library. You each mostly just want to spend time doing your own research alone with as few responsibilities as possible. But you also need to make this work because if no-one does any of the duties then no-one will be able to conduct research. The real world constantly wants you involved and getting research material requires you to go out into the real world. This pitch works best if you and your group are already familiar with academia.