Theres two main differences. One is Legit, The other is Illegit.

Legit, generally mean's good. Obtained with the right intentions and went the right way of obtaining it for e.g "I made 10 dollars today from working" is Legit.

Illegit is taking the nub way out. No using the right intentions to get it. For e.g "I stole 10 dollars from this shrub who just got payed from work".