¿Cuál es la diferencia entre I will finish my work by 5 o'clock y I will have finished my work by 5 o'clock ?Puedes dar oraciones como ejemplo.

They're both completely correct, but to sound more natural you would just use them slightly differently.

'I will finish my work by 5 o'clock' sounds like a solid sentence on its own, you don't have to add anything to it.

However if you say 'I will have finished my work by 5 o'clock' it feels like you need to modify it. For example 'I will have finished my work by 5 o'clock, so we can go out after that.' or 'I will have finished my work by 5 o'clock, so I'll have plenty of time to watch television'

but the difference is not big at all, they both technically mean the same thing :-)