I've played Sims 2 for a bit and I've modded in some things but I've been having trouble with meshes for the past two days. I'm getting to my wits end and it's frustrating. I've added some extra stuff to make some Sims in my desired style and yet, they don't want to show up.

I really need some help with this.

I'm using some of Atreya's ear and tail meshes along with a snout one I found. They're not showing up. Please help.

First of all, you're a bit better off asking in the help section, as this is the creation section. A moderator can probably help move the topic for you.
The help section is in the Sims 2 "Community Forums" --> "Sims 2 Help" - here: https://modthesims.info/f/31/

1: If they're showing up wrong, are you sure you put in the mesh files and not just the recolors?
2: If they're not showing up at all, are you sure you put in at least one recolor for each mesh? (CAS meshes don't show up without recolors)
3: Have you unpacked zip/rar files? (With very few exceptions, you should only have ".Package" files in the Downloads folder)