Queing for matches can be anywhere between 15 seconds to 5 or 10 minutes based on how many maps you Q for. The more maps you select the faster you will find a game.
Your mmr is the level of difficulty the missions will be. It is averaged among all four players. Starting out your mmr will be low (20's probably) and by winning missions it increases, losing decreases. Above 50mmr is widely considered high mmr so enemies in missions starting at 50mmr feel a bit more bullet spongey and there are more of them.
Being carried is just something that will happen at times and its best not to worry too much about it. This games matchmaking has a tendency to throw level 1s in with 3 300+ lv players often enough and a level 1 just wont be effective. Use that time to feel out the combat and level and observe your allies while trying not to die every 15 seconds because the team shares lives
Welcome to Spacelords!