Wednesday’s opening day of summer league practice for the Nets was new coach Jason Kidd’s first day on the job. But it also marked the first day on the job for Nets first-round pick Mason Plumlee, who took the floor for the first time as a pro after signing his contract with the Nets about a half-hour before the morning practice session. “It was very exciting,” Plumlee said of signing his first contract. “It’s nice to have that out of the way. I didn’t plan on it taking very long. My agent and [general manager Billy King] worked through it very quickly, so it’s nice to have that done.” The 7-foot center is expected to be in the starting lineup for the Nets’ entry in the Orlando Summer League, with the team’s first game coming against the Pistons on Sunday at 5 p.m., when he’ll play alongside second-year players Tyshawn Taylor and Tornike Shengelia — the three participating players who are expected to be on the team next season. All three will have to adjust to a new coaching staff. “I think we’ll find out a little more each practice,” Plumlee said, adding that a good portion of practice time was spent going through various terminologies they would need to use. “I thought Tyshawn played very well today. But, yeah, we’ll see. We did a little bit of live stuff, but most of it was just walkthroughs.” After playing four years at Duke, including averaging 17.1 points, 9.9 rebounds and 1.4 blocks as a senior last season, the 23-year-old has been billed as potentially ready to step in right away and contribute to an NBA team.