When a person dies here on earth, Catholics believe that their soul continues to live on, separates from the body and goes to be judged by God and is sent either straight to Heaven, or to Purgatory for a time of purification after which it will definitely go to Heaven, or straight to Hell. The body is no longer living at that point and is either buried, or cremated and interred, in the cemetery. The soul, which is essentially the living person at that point, isn’t in the body and thus isn’t in the grave or the columbarium niche. We do respect the body because we believe that at the end of the world. God will raise/ reconstitute the deceased earthly bodies, perfect them, and infuse all the souls back into them at that time. Therefore we would not deliberately walk on graves or do other disrespectful things.
Regarding visiting a cemetery, you can converse with your deceased loved one from anywhere. Some people like to visit the cemetery to do this because of the proximity to the bodily remains or because it’s simply a quiet, peaceful, pretty place geared towards remembering the deceased. Catholics can also get indulgences for visiting a cemetery and praying for the dead, which they often apply to the deceased in hopes of helping them get out of Purgatory or have an easier time in Purgatory while they’re there.
For 25 years after my dad’s death, I did not visit the cemetery where he was buried. I didn’t want to revisit the bad memories of his death and I figured he wasn’t in the grave, so why go there when I could just talk to him from my room at home or wherever. After 25 years my mother died and I returned in a big way to active Catholic practice. Within the few years after Mom died, I started to also have a lot of friends and other loved ones including my husband and other relatives die, and I also started serious indulgence practice with the goal of giving all indulgences to help the Poor Souls in Purgatory (including but not limited to all my dead loved ones). So I started spending a lot more time in cemeteries, including the one my parents are now both in. At this point I will sit and talk to them at the grave, pray for them and everyone in the cemetery, and also think about the day when I plan to be buried in the same cemetery.
As for conversing with dead loved ones, it’s a normal thing for Catholics to do because we believe they are still living and have hope that they are in Heaven or at least in Purgatory. We don’t try to conjure them up, we don’t ask them to predict the future for us, we just talk to them. “Hi Dad, how are you doing, I hope you’re in Heaven having fun with Mom, I have this and that going on in my life, please pray for me, I was thinking of you yesterday while watching the ball game and remembering how we used to watch together” etc. As I said, we don’t need to go to the cemetery to do this, and we realize that God is the one who determines whether they will “get the message” or not but I trust that God would be amenable to this sort of chit chat which manifests Catholic belief in the afterlife.