The feminine and masculine
I'm new to learning french and i don't understand why some are masculine and some are feminine like bleues (feminine) bleus (masculine) i don't understand can someone explain?
I don't think there is a real reason as to "why" there are genders, only that in the French language it influences a lot of things. For example; verb endings and adjective endings change depending on the noun gender, as well as the pronoun used before the noun.
Duolingo has some notes on the genders in the first couple of lessons, but if you want an external source, there's one here. :)
Those are just ways to describe how to use some words. They do not refer to the gender of the people or thing described.
For example, we say "une tomate" a tomato but "un gâteau". "Tomate" is feminine so we use "une" for 'a' and "la" for 'the' etc.
For "gâteau" we use "un" which is the masculine for "a" and "le" for 'the'.
There will be other differences also as you have seen with bleues (feminine) bleus (masculine).
The best advice I ever got for any new language was to learn the genders from the start so that later you don't have to worry about them. And with French you're lucky; there are only two genders other languages have three.
So, if you see "la" it means feminine and "le" is masculine. Look through the words you've learned so far and note the differences.
Historically some French words derive from Latin words that were masculine or feminine
The languages humans speak now have evolved through generations - it's natural. You can't scientifically question why we call the color blue - 'blue' (why have only those letters been used? Why this exact composition of letters? and so on). The same goes for grammar - which includes the questioning of the existence of genders.
To answer your original question, here are 2 points:
You could say that many languages were actually derived from other, older languages which used genders.
But if you were to ask again why this ancestral language used genders in the first place - there is no exact answer. (At that time, communication itself may not have evolved so much that people those days would even document how their language came to be the way they used it.)
But most importantly, it's not just French. From Arabic to Hindi, a diverse range of languages across the globe use genders. Some have 3 - others have none.
So I guess you just get used to it - the others have already provided good links to start with !