1 How import still image
Just add image into Media pool, each image will be exactly one frame, if you import image which has more than one frame, you might import your images as image sequence. Images will be treated as image sequence in same folder has sequential number in file name as postfix. When you import files, there is a check box to turn it off.
To configure the duration for still image, go to Davinci Resolve Preference -> Editing -> User -> Standard still duration.
2 How to copy transition from one clip to another
Press Alt and drag transition to target clip in timeline.