One likes to drag small donkey over river (6)
I believe the answer is:
smoker
'one likes to drag' is the definition.
I can't tell whether this definition defines the answer.
'small donkey over river' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'donkey' becomes 'moke' (moke can informally mean a donkey).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'river' becomes 'r' (abbreviation for river).
's'+'moke'+'r'='SMOKER'
Can you help me to learn more?
(Other definitions for smoker that I've seen before include "one cures" , "part of train once" , "Tobacco user" , "Puffer" , "User of cigarettes" .)