수집 is a noun hanja word that means 'collecting certain materials for a purpose'. It can be also used as verb, like in 수집하다.
수집하다 means 'collect certain materials for a purpose'
모으다 is a Korean verb for 'collect (something with or without purpose)'
ex)
I collected garbage.
쓰레기를 수집했다 is awkward
쓰레기를 모았다 is OK.
I collected stamp.
우표를 수집했다 is OK.
우표를 모았다 is OK.