Learn French: Ce sont des stylos et des crayons.

In French, you usually cannot leave out the article (words like a, an, the, or some) before a noun. Des is the plural of un or une. While in English we can just say "pens," in French you need des stylos (literally "some pens"). You also have to repeat the article for every noun in a list, which is why it is des stylos et des crayons.

Do I pronounce the s at the end of stylos and crayons?

No, the s added to make a regular noun plural is almost always silent in spoken French. You only know the word is plural because you hear the word des right before it!

Why does the sentence start with Ce sont? Shouldn't "These" be a plural word?

Ce sont is the plural version of c'est ("it is" or "this is"). Even though the things you are pointing at are plural (pens and pencils), the pointing word ce stays singular, and the verb changes to match the plural items: sont (are). So, ce sont is the standard way to say "these are" or "those are" when identifying things.

How do I know if a noun gets an s to become plural?