Hello!
A short time ago I was gifted a little juniper bonsai tree by a family member. I've done some research but I'm still very new to this wonderful world of bonsai, so be gentle with me please. I have some questions about pruning and shaping my tree.
It was given already in a kind cascade shape. (I can't really say cascade because the trunk doesn't grow upward or arch before flowing down) Does it have to maintain that shape? Or can I change it?
And if I could change it, how do I decide what to change it into? Do I just look up pictures of junipers and choose a style I like? Or is there a certain ways junipers should look?
What resources can I find to tell me exactly how to wire and prune? I'm concerned about hurting it.
Thank you for your help!

This just a young plant that looks to be growing quite well. I hope it is outside in the sunshine and not inside. I would suggest buying a book there are many good ones around and learn how to keep the species first then you can do the other things. The style can be changed at the moment it is not styled, that is ok as it is not ready. Water and sun is what is needed. Next year once you have found out how to prune then you can start to style. Don't assume it has to be re potted, check to see if it is root bound first, and not until next spring.

This is very good advice! Thank you! For some reason I was thinking it needed to be shaped young so that it could grow well in the future, but I guess that isn't true.
I did read though that if it was bought planted in cheap soil, it could be moved to a new pot the following spring or growing season. Is that true?

The soil just needs to be free draining it does not matter what it consists of so much. If the plant is not root bound and drains well then there is no need to re pot. If it does not drain well then yes in the spring it should be re potted.
I would also suggest that you see if there is a club near you where you could get advice as it is very difficult to say what needs doing from a picture seeing only one side.

Thank you!

Do you have any specific suggestions for pruning/shaping books, or bonsai in general? And at what age do people usually start shaping them?
I'll take that advice about the club, but here are some more pictures anyway. ^-^

There is no specific age of the tree to start prunning and styling. What you need is to let the tree grow until it have health, and enough size and amount of branches to support your final vision for the tree.