participle ends with -ED... studied, confused, etc.
gerund ends with -ING... studying, watching, etc.
gerunds placed with TO BE by their side are VERBS:
I AM STUDYING
so use those to mean an action
gerunds also can be used as a noun and DO NOT imply action:
WATCHING TV distracts you from STUDYING.
so in both cases these are used as a subject/object and don't imply an action -> gerunds
participles usually are the Past form of the verb
I STUDIED
so use this when talk about simple past...
sometimes gmat ?s start with participle in a phrase:
Studied hard for GMAT, I got a good score. -> Studied here describes "I"
hope others add more to this.