hello there! :)
Organic chemistry deals with the functional groups so there are lots of things to keep in mind.
to understand the subject better, first we need to try to identify the functional groups and lists them down.
try to make a a table of all the functional groups togethere with its nature of reactions and write down the specific reactions that your teacher told tyou.
some of the functional groups are:
alkanes, alkenes, alkynes, cycloalkanes/enes/ynes, alkyl halide, alcohol, amine, ether, carboxylic acid, esters, aldehyde, ketone and amide and aromatic compounds
each functional groups is different from each other. they have different nomenclature and reaction.
by this time you can now identify them during exams or quizzes. For example, a certain reaction is only allowed for alcohols and not for carboxylic acids.
hope this heps :)