In a nutshell, spawn in the world > go build house (optional) > go caves or villages > find gold chests > get accessory (Hermes boot, Cobalt shield, etc...)> get armor > fight boss > get their soul thingies > build stronger weapons > modify the weapons by spending all of your limestones on an anvil > get a legendary modifier > fight more bosses > get a mount (because **** it) > fly around the world with the mount > find the 12 somehow different eyes that all require different things (Some in tombs, chests, villager trade, etc...) > go to end > wtf what happened to the ender dragon arena > pray you can win against the ender dragon > win > go to the nether for whatever reason > fight the literal world ender > get one shot, becuz he's bs > fight the more stronger bosses > suffering > repeat.
I gave you a very basic, nutshell breakdown of one of the ways of what could happen.
Now, a normal explaintion. For starters, you know how terraria has modifiers for items? Like Menacing, Warding, Hasty, etc...? Well, weapons have those here, altho there is more stats now (IIRC)
Additionally, like terraria, a lot of the good weapons are hidden behind the materials that bosses drops.
There is also an accessory/artifact system, which is similar to terraria's. Look around the world, find a chest, get an accessory (IIRC the modpack has huge similarities to terraria when it comes the artifact system). Said accessory can speed you up if you keep walking, cool. Other accessory removes fire damage (I think it was literally called Obsidian Skull, just like in terraria).
The weapons are also very fantasy-like. One of the weapons was just straight up wukong's staff. It has 3 abilities, one of them was litearlly just making invulnerable for a while, with you not being able to do anything. Thing is, you can use it when you are falling, so it is pretty good to prevent that, and it also has whirlwind modes and stuff.
Overall, the modpack honestly has taken things from both Baldur's gate/Diablo3, and Terraria in a way. I think you'd get used to it, honestly, as someone who played terraria a lot, the modpack isn't that confusing. I think it was the first modpack I played when I got my new laptop (This is like, a year or two of not playing modded minecraft), and Prominence was pretty chill, you can just do whatever you want, follow the quests for rewards, or just go to caves, villages, etc... to get artifacts and see what is good or not.
It is fun, really, and there is no tech stuff that is going mess with your brain or anything. Just pure fantasy, and bosses.