What is the difference between le and l' in french?

'le' and 'la' are the two French Words which correspond to the English Word 'the'.

'le stylo' :: 'the pen' (usually, but not always, a biro)

'la plume' :: 'the pen' (usually, but not always, a fountain-pen)

French needs two Words for 'the' because its nouns all have grammatical gender (a feature which is absent in English).

le stylo, le soleil, le violon :: the pen, the sun, the violin

but

la plume, la lune, la guimbarde :: the pen, the moon, the jawharp

When 'le' or 'la' precede a Word that begins with a vowel, they shorten to 'l'

''l'alouette' 'the lark' (NOT la alouette); 'l'opposite' 'the opposite' (NOT le opposite).

So there is really no difference between 'l' and 'le' in French. 'Le' becomes 'l' when the next letter is a vowel.