This was a learning experience.

Tuesday’s preseason opener against the Boston Celtics gave the 76ers a sense of where they are as far as preparation.

The Sixers returned just seven players from last season’s underachieving squad. They have a new coach in Doc Rivers and a new coaching staff and key veteran newcomers in Seth Curry, Danny Green, and Dwight Howard.

So this game was about seeing where the Sixers are with the things they put in, and figuring out what they don’t like.

“Conditioning levels, where guys are at,” Rivers said before the 108-99 victory at Wells Fargo Center. “Confidence levels, where guys are at. Timing. There are so many things you can get out of these games.”

But perhaps the biggest question was how would the Sixers look offensively.

Initially, they looked a little ragged with their motion. They looked just like they are: Players still trying to get familiar with each other.

“I thought we established our pace overall,” Rivers said. “I think Ben [Simmons] one time was walking the ball up the court and jumped up, just the pace alone puts pressure on the other teams.”

Rivers is trying to get the Sixers to understand that their towering size combined with pace creates force and makes them tough to guard in the open floor. He was happy with their open-floor game, but wasn’t thrilled with their execution.

“But you know, first game you can’t expect everything,” he said.

However, their spacing was good. They were also sharing the ball, which enabled them to get a lot of good shots.

Joel Embiid benefited the most. The star center also took most of the Sixers’ shots. At one point in the second quarter, Embiid had 12 shot attempts while the other four starters had a combined 12.

He only played in the first half and finished with 18 points on 6-for-14 shooting to go with 3 rebounds, 2 assists, and 2 steals in 17 minutes. If there was a negative, it was his going 0-for-4 on three-pointers. Embiid did not speak to the media following the game.

“He’s phenomenal,” Rivers said. “It’s a great example for Joel. We ran our stuff, but we didn’t run his stuff and he still had 18.”

That’s one of the things that Rivers has been telling the three-time All-Star in training camp. He informed the big man the Sixers can run a continuity offense and not run any plays for him. But he’s still going to end up with the ball due to being the best player.

“I thought that was a great thing for Joel to see,” the coach said.

It was also easy to see why Rivers had been raving over Shake Milton throughout training camp. The third-year guard looked like he could be the bench scorer and facilitator the Sixers would need to be a contender in the Eastern Conference.

Milton displayed an ability to drive the lane and score or find teammates. He also was hot from three-point land while running the offense as the backup point guard. Milton was hot in the third quarter, scoring 15 of the Sixers’ 32 points. He made 3-of-5 three-point attempts in the quarter en route to a game-high 19 points.

First-round rookie Tyrese Maxey took over where Milton left off after entering the game in the fourth quarter. The rookie displayed the floater that he had success with at Kentucky. Maxey finished with eight points on 4-for-6 shooting and three assists while playing 12 minutes in the fourth quarter.

“I think the main takeaway I took from this game is that I can play at my own pace,” Maxey said. “I dictate pace offensively. When I’m on the ball, Ben told me, I don’t have to play too fast. I don’t have to play too slow. I can play at my own pace. I think I did that.”

For the first time, Rivers came into the Wells Fargo Center as the home coach, and it wasn’t the same.

“When I got out of the car, I didn’t know where to go, obviously,” he said. “I have been going through the loading dock for 34 years, I guess, so I didn’t know there was another entrance. So that is different — just knowing the lay of the land.”

He said it’s nice to have this preseason opener to get his feel for how things are done at his new home arena.

But in regard to basketball, he said it was good for him to get a feel for where the Sixers are.

“It is tough to judge you versus you, and we get a team like Boston to come in here, it’s a good test for us,” Rivers said before the game.

The Celtics swept the Sixers in the first round of the last season’s playoffs. That led to the Sixers firing coach Brett Brown and restructuring their front office.

The Sixers had a moment of silence for John Smallwood, who died Dec. 6 after a long illness. Smallwood, a longtime sports writer and columnist for the Daily News and later The Inquirer, was 55.

The Sixers and the Celtics took a knee during the national anthem before the game. NBA players began kneeling during the national anthem at the beginning of the NBA restart in Kissimmee, Fla. The players are doing this as a way to use their platform to make a statement about racism and social injustice.