Any easy Algorithm for prime numbers?

I'm making a program in Javascript to check if a number is prime or not. But I don't know the right algorithm to do it.

Believe me, I researched a lot in google but most of them just seem hard to understand(I'm not an english speaker so scientific words are hard for me to understand)

Any easy algorithm to check if a number is prime or not?

Also, don't give me the direct code, just tell me the rules of the algorithm/way and I'll apply them myself to code.

And please don't close/remove this post like what happened with all my past posts.