I'm novice at French but here is my best try.
livre means book. Book is a masculine word in French. Since there is -s, it is plural.
So,
Les livres
stylos means pens.
It is plural so just like livres,
Les stylos
crayons means pencils
It is singular so we depend on the gender of the word. Crayon is a masculine.
Le is for masculine
La is for feminine
Les is for plural words (most if not all)
l' is when there is a vowel on the start of a word (usually).
Le crayon
Montre is watch in French.
It is singular and is a feminine word.
La montre
sac à dos is bagback in French
It is singular and is a masculine word.
Le sac à dos
Now complete the whole paragraph.
Les livres, les stylos, le crayon et la montre dans le sac à dos de Marie sont tous neufs.
