I am having the main protagonist find their imaginary friend that they had previously forgotten. How would I make some flashbacks without making the plot too confusing or sounding choppy and forced? How would I go about this in such a way that the reader will understand what's going on, without boring them? What point of view should the flashbacks be in?
Like @Ceramicmrn0b says, you have to make the flashback obvious. it should be in a different paragraph for starters, maybe even after a page break. If you want to go all-in, you could possibly do a new chapter if your book is structured that way, but I wouldn't recommend it.
As for the point of view that you choose, that is entirely up to you. YOu can read books with flashbacks in them, (like one of my personal favorites, Flowers for Algernon) or just dive in ( a good link to check out is this one, it explains the flashback a bit). A word of advice on whichever POV you choose: Don't use second-person POV. It's very confusing jumping into another point of view (I'm guessing) and having it so starkly different from your book. Most novels are written in first or third-person point of view, and I would keep it that way for the flashbacks--unless you have good reason not to.
The bottom line is this: Make the flashbacks obvious and make them separate. after those two things are done, you have a pretty good start to a flashback.
If you want to do the flashbacks, make sure the reader knows that it is a flashback. I would do this with a line of a few asterisks and then begin flashback and end the same way, this way it has a very clear end and beginning of the flashback.
I wouldn't do really short flashbacks this way, in which case you should say something along the lines of 'Bob suddenly remembered X, the images flashing in front of his eyes. (insert remembered thing here)'.
The book 'The Last Thing I Remember' by Andrew Klavan does these flashbacks really well and might be worth a look.
When you write a flashback, keep these rules in mind:
#1: Do not switch POV
#2: Make it absolutely clear when the flashback begins, and when it ends
#3: Keep it short
#4: Do not use too many flashbacks
Rule #1: It is very confusing if you switch POV (3rd perspective becomes 1st, 1st becomes 2nd, etc.) for a flashback. Your readers will struggle to understand what is going on. Try and stay consistent in POV..
Rule #2: One way you can do this is by using an emotional trigger. The trigger could be an everyday object or word, and when the character sees/hears it, they go back to a memory. Think about when you are suddenly pulled into memory. An encounter on a snowy day with an ex could prompt a memory of a ski trip taken together; the smell of daisies could remind a character of her wedding; etc. Then, you could also use a trigger to pull the character back to the present.
Rule #3: Long flashbacks are boring and take away from your story. Do a favor to your reader and keep your flashback short and succinct.
Rule #4: A flashback should only be used when there is no other way to get important information across to your reader. If you use it whenever you want to incorporate a piece of character background - your readers will be confused about which plotline they should focus on. If you use too many flashbacks, your main plot will not feel as essential to the reader and the whole story will be less engaging.
So, follow the above rules, and you should be able to write a good, structured flashback.
Good luck with your writing!