Sweater tips?

I’m a beginner knitter and I’m currently knitting my first ever sweater - the Haptic sweater from we are knitters. Tbh the pattern isn’t super descriptive, and I have 2 questions:

  1. Do I need to block the sweater before or after joining the pieces together? Do I have to block it at all?? I’ve never done this before, but I’ve seen people post about doing it.
  2. Any good YouTube links for joining the pieces together?

Thank you!!!! Hopefully all goes well and I can post a picture when I’m done!!! :)