Prepositions are used to link words. They don't have a meaning on their own. The preposition de is used in many different ways. Here are a few examples:

to express what something is made of (materials)
pastel de queso - cheesecake
jugo de manzana - apple juice
diente de leche - baby tooth

to explain what something is used for
pasta de dientes - toothpaste
salón de belleza - beauty shop
la pelota de playa - beach ball

to express origin or who it belongs to
Palacio Nacional ciudad de México - National Palace city of Mexico.
Día de la Madre - Mother´s Day

to accompany a verb
acabar de - to have just (verb)
El pájaro trata de volar. - The bird tryes to fly.

for dates and time
Hoy es 5 de marzo. - Today is March the 5th.

Example sentences:

Este es de seda, ese es de algodón. - This is silk, that is cotton.
Soy de Nueva York. - I am from New York.
Yo iré al partido de fútbol con ustedes mañana. - I will go to the soccer game with you guys tomorrow.
Tengo los pies de mi abuelo. - I have my grandfather's feet.