The difference is that the first one is right and the second one is wrong. 'I'll be working' is the future continuous. 'I'll working' is a form that doesn't exist. And don't forget - the pronoun 'I' needs a capital letter.

You can say: I'll be working late tomorrow or I'm working late tomorrow. These two sentences mean the same thing.

The second one is not possible to say (you can of course but makes no grammatical sense). As for the first one I believe it's correct.

Rephrase your concern: I will be working later on I will work later on