As the title says, I'm wondering how long it usually takes for a post to be approved. I'm new when it comes to uploading on the site, so I'm not sure what to expect. I noticed someone already gave my post a score, but didn't approve or decline it's approval. Any responses would be greatly appreciated :)

The approval time varies, based on how much of a post backlog there is to be approved and how much time the volunteer mods are able to devote to this site.
The score comes from other users giving a post an upvote, not from mods. As a user, you can upvote other posts too, and favoriting them automatically gives it an upvote. You can search by score too, by adding "sort:score" to a search (without the quote marks). For instance, the search "sort:score breasts" shows you all the posts tagged with "breasts" in order of highest score. You can also just search "sort:score" to see the highest-scored posts on the whole site!