IVI is the first person perfect (past tense, completed action) of EO (I go); therefore IVI means "I have gone". ILLUC means "there", so ILLUC IVI means "I have been there".
FECI is the first person perfect of FACIO (I do, or I make); therefore FECI means "I have done" or "I have made". ILLUD means "that", so ILLUD FECI means "I have done that".
In short, "been there, done that".
For the Latin scholars who've forgotten, IRE and FACERE are irregular:
EO, IRE, IVI, ITUM
FACIO, FACERE, FECI, FACTUM