Matchmaking in norms

First off let me say this. I have no idea how MMR works in norms. Now for about 3 months straight I did nothing but teams of 5's in norms 'cause I don't really like ranked. I mostly play league to play with friends. Our teams consisted of mostly golds a plat and myself unranked. A few of my friends went on vacation so I've been forced to play by myself or with one of my gold friends (I haven't done a full group in a while now) and it's been going fine so far. I'd occasionally see a diamond on my enemy team but most of the time my enemy teams in norms would be plats and golds while my team was just golds and myself, unranked. I could deal with that. I won some I lost some. Then there was a sudden change two days ago. In a total of 7 games over two days I have seen a diamond or multiple plats on the enemy team while my team remains golds and now silvers. I just don't get this matchmaking is what I'm trying to say. I don't understand MMR and why I'm fighting these people when I was unranked for so long and am now silver 5 (do to choice. I really hate ranked with a passion and only did my placements because of pressure from friends and 5/10 of my placements had an afk from level 1 so I went 5wins/5losses. I'm sure if I put the work into ranked I could get low gold but that doesn't explain why I'm fighting high plats and low diamonds constantly while my team rarely sees a diamond and is mostly high to med golds.)

If anyone has been experiencing this in norms let me know. Or if you know how MMR works in norms and could explain it to me that'd be cool too. I'm mostly ranting about this because I go to norms to practice new champs like my most recent skarner jungle and it's really hard to practice against people who severely outskill me. Sometimes I feel like the only place I can safely practice where I feel the teams will be balanced is in ranked but I know ranked is no place to practice new champions and like I said before.. I really hate ranked with a passion.

Edit: This is not team builder. It's in normal norms.