Trackpad not the same after hardware reinstallation

Hi all, I had problems with my MacBook and had it fixed at the Genius Bar. Thank you!! Now, however, I am trying to drag a jpeg from my desktop to the Pages app so I can do some creative stuff. LOL. I was always able to tap, highlight the jpeg file and drag it to wherever. Now the pic opens in the Preview app. I'm not able to drag it. I even went to System Settings to change some stuff but I still can't do it. I have no idea what I changed when I first got my Mac 5 years ago. All I want to do is tap/click and drag. I thought I'd try holding down the lower left corner of the trackpad with my left thumb and then drag with my right pointer finger, but this did not work. I am clueless. Can anyone please advise? Thank you in advance.

PS - I am also having trouble dragging files to the Trash!!! Oh my goodness