The story I beta-read was just in g-docs, with the questions placed in-between each chapter.
If you're willing to dish out the same to another, you can effective get a crowd editing service for "free" over on Reddit at /r/DestructiveReaders. Quotes around "free" because you have to destructively critique another author's chapter first if you want it done for yours.
So, for beta'ing I'd be willing to assist, at least for a few chapters. Dedication to continuing would rely on the quality of the story. For example, Westerns aren't exactly my cup of tea but I could stick around for something that isn't very poorly written. If I genuinely think it's hopeless, I'll be honest about it.
If you want to take me up on it, I will happily give honest constructive criticism. May request reciprocity for my own future projects.
The purpose of editing is to churn the words and ideas of the author into something that's understandable and enjoyable for the reader. The baseline you can expect from asking random people is for them to correct any misspellings and fix some minor grammar issues. Depending on how much you trust your editor, they might even reword or rearrange some of your sentences/paragraphs in order to make the words flow better.
Now, a good editor will also point out where your ideas aren't working. They might highlight parts of your work that are vague or that don't convey what you intended. They might suggest deleting scenes that make the story feel worse, or they might suggest that you add more scenes to something in order to bring an idea together.
This also means that you and the editor have to balance the intentions of your writing with the enjoyment of the reader. They might suggest things that you don't like, and you have to evaluate whether or not it's worth changing.
Do you need an editor? If you're confident in your ability to write and have the courage to rewrite things that you know aren't working, then not necessarily. Everyone benefits from having a second eye, though, so if you're able to self-edit all you might need are some friends to beta read and point you in the right direction.
As for where you can get an editor... I'd say that it's better to have no editor than a bad one, so you'd want to look for someone who is either also a writer, or who reads a lot and has a good understanding of what makes a story work.
When you browse some of the most liked works off places like archiveofourown, a fanfiction site, you'll find that many of them are complete, novel-length stories of surprisingly high quality. That's because a ton of great writers gathered together under their love of whatever fandom they write for, and formed tight niche writing communities where they all help each other out. You'll find that in most stories the author credits another writer (or several) for beta reading and editing for them. In turn, the author is often credited by other writers for helping beta read or edit as well.
In summary, you're likely to find some great editors in other writers, because they'll be able to see if your story is working and have the skill to suggest how to fix or adjust if it isn't. If you want an editor you can trust, you'll have to build a good friendship or partnership. Or pay them. :q