Welcome!
I've only been a "charmer" (as they like to say) since January myself but will try to at least point you in the right direction. Unless I'm still missing a hidden shortcut myself, to write reviews you actually have to go to the shop & find each individual product yourself. Definitely nothing that will win for convenience or ease-of-use, but not horrible once you get used to it. The products from the most recent boxes are usually listed first (& the previous month's next, & so on) which I find definitely helps. The advantage to this non-user-specific set-up (or, perhaps more accurately, lack there of) is that you can review - & receive charms for - items you have knowledge of/ experience with from somewhere other than your boxycharm. You can also receive points by pinning or sharing products on social media; there are little prompts by each sharing icon that tell you the exact # toward the top of each product page. Sometimes there is a bit of a delay in a given month's items appearing in the shop and, as such, being available for review, but there is no deadline by which you must do a review in order to receive points so this isn't really a problem.
You also receive 450 points every 3 months you are continuously subscribed, but it's a bit goofy in that this occurs 90 days after you initially subscribe rather than upon billing for your 3rd box; in practice this means that this bonus occurs closer to when you receive your fourth box than your third but it does occur nonetheless. Like with most subs you can also receive points for referrals subs.
As for what you can redeem your charms/ points for, it leaves a bit to be desired as there generally seem to be only 8-15 items available & the best goodies "sell out" fast. Most items appear to be from previous boxes & upon redemption your item(s) is included in your following month's box.
Hope this helps a bit. Additionally here's the link to their charm-specific FAQs:
https://help.boxycharm.com/customer/portal/topics/693925-charms/articles.
Don't hesitate to ask if you have any other questions.

Melissa
P.S. I recall having trouble finding where to log on to the boxycharm site initially; it's quite odd but it's a tiny icon all the way @ the bottom, a bit right of center. Once you're logged on you see a menu w/ options for your charms, billing, account info, etc.