There was no attempt at any coherent plot on this episode. The group sang a bunch of Britney Spears songs and they sort of helped everything feel more powerful in certain areas of life.
For example, Rachel hesitated about having Finn rejoin the football team - which the coach allowed after witnessed Artie apologize for getting him kicked off - because she thought they both had to be losers in order to make the relationship work. But she then realized she could trust her man. (And it helped when Quinn came on to him, only for Finn to turn her down.)
We also met Carl, Emma's dentist boyfriend. He asked Will to back off his pursuit as long as he was dating Emma, but Will didn't really listen. He tried to be more cool and spontaneous in order to win Emma over, only for her to later say she doesn't want Will to change. Just to relax. It didn't help him to do so when Terri showed up and said she thought they'd eventually get back together.
That was about it. The Britney impersonations were cool, but they didn't really connect to the story in any way.