When you want to describe a certain type of person, you can do it like this:

I need someone strong to help me move it.

In that example, you're talking about a "strong" person. But another way to describe a certain type of person is with a sentence, like this:

I only want to work with someone I can trust.

In this case, "I can trust them" describes the kind of person that you're talking about.

You can also include "that", "who", or "whom":

I only want to work with someone that I can trust.