Particles are little grammar things that you put in your sentence to make it make sense.
They are used to indicate what role the word has in relationship to the other words in the sentence.
For example, in the sentence I eat bread
I - the subject eat - verb bread - object (the item you are doing the action to)
In japanese, particles are used to denote I is the subject of the sentence etc.
The の particle has two main uses: 1- possesion To show something belongs to someone (mine, yours, his/hers).
the pattern is: person の item
E.g わたし の ペン my pen
あなた の ペン your pen
みきさん の ペン miki's pen
2- modify nouns modify nouns is when you use one noun to describe another noun.
e.g japanese book (book is the main thing, and it being in japanese is the describing attribute)
the pattern to use: Noun1 の Noun2 where noun1 is the attribute describing noun2.
E.g。 日本語 の 本 a japanese book
you can also use this for people:
つま の みき my wife miki (wife being the main thing, the name miki being the describing attribute)
if you are using it for this purpose, dont get confused, it would not be translated as miki's wife (possession, use1), but as the wife that is miki (noun modifing, use2).