Your chosen team now wants you to muster with the other new folks and run the gamut of some sort of "Orientation Program" or "Trial Period".
Really?
You're a grown adult, have been playing and read the information on forums and build-specific posts; you KNOW this stuff! Now you have to go through a couple weeks of orientation??
Allow me to explain; while some balk at starting in the Training Room, please understand we don't know you, and need time and a venue to get you in-game. We'd like as many of our members to greet and get to know you. In part it IS a BASIC evaluation, as all units have some standards that they'll regret not measuring of all new members if they just hand you the keys from day one. You'll want to see if these folks are what you expected. Both you and the unit are testing, "Goodness of Fit" for you as a part of them.
Then there's the "team" thing...
One unwritten goal of orientations I have been in is that the unit, if they're organized ad goal-oriented, know what they need individuals to be able to accomplish. While they like your color scheme and compliment your mechs' fine maintenance record, what they want to know is CAN and WILL you be able and willing to perform in the 12 man teams that Community Warfare is guiding us to. Being the BEST Solaris champion won't mean much to a House wanting to capture a planet if you can't carry the team. Unlike All-Star basketball, teams are more dependent upon everyone being equipped and thinking as a TEAM, not 12 individuals. Orientation Programs often include some means of explaining and mentoring the new pilot to what the team feels they'll need and expect. In some cases this means build standards or preferences. Other units may include movement and communications, some battlefield assessment or the like. Most I have seen offer training if you want or would just like to see what they've come up with that you weren't aware of.
Ask. Don't be quiet, hoping to slide by; this is important to your enjoyment of the game in these teams. These units will have concrete goals now, not just statistics and bragging rights. They want to excel, you want to be a part of it, so find out what they're looking for and make sure you get the proper instruction and guidance.
...And try to have fun. Winning is Fun. Winning as part of a Team is More Fun. Seriously.

Oh, and Consider Turning to the Dark Side.