This is because of a limitation in R which does not use multiple processor cores by default for many functions.

So, in a modern computer, (almost) all of which have multiple cores, you can increase performance by writing code that uses those other cores.

If you use the *apply functions (lapply, sapply and so on) they actually will use multiple cores. But if you write a loop, such as a for() loop, it will not.

This is all actually explained in the link you provided. So perhaps some of your challenge is an understanding of IT. If so, perhaps we could start by answering domain knowledge questions. Is any terminology unclear? Descriptions of how R or computers operate?