1.
If you hand in something such as homework or something that you have found, you give it to a teacher, police officer, or other person in authority.
I’m supposed to have handed in a first draft of my dissertation...
My advice to anyone who finds anything on a bus is to hand it in to the police.
PHRASAL VERB : V P n (not pron) , V n P
2.
If you hand in your notice or resignation, you tell your employer, in speech or in writing, that you no longer wish to work for them.
I handed my notice in on Saturday...
All eighty opposition members of parliament have handed in their resignation.
PHRASAL VERB : V n P , V P n (not pron)