Ensuring that verbs agree with their subjects is a problem that less-experienced writers frequently have and, while it sounds complicated at first, the truth is that it’s a fairly simple problem to fix. In English, (and Latin and Spanish and some other languages) verbs have to be “conjugated” to reflect the person, tense, and mood being used. It’s easiest to see as a chart:

.SingularPlural
First PersonI amWe are
Second PersonYou areYou all are
Third PersonHe/She/It isThey are

This is the present tense English conjugation of the verb “to be” with the singular (one subject) on the left and the plural on the right. The simple past tense looks like this:

SingularPlural
First PersonI wasWe were
Second PersonYou wereYou all were
Third PersonHe/She/It wasThey were

Here’s the trick. If you aren’t sure if your subject and verb agree, think about a person who speaks English well (your instructor, a well-spoken public figure, or someone you know who is well-educated, or [if you can’t think of anyone] Neil deGrasse Tyson), then read the sentence out loud and see if it sounds like something that person would say. Dr. Tyson wouldn’t say that “[w]e is part of this universe,” he would say that “[w]e are part of this universe; we are in this universe, but perhaps more important than both of those facts, is that the universe is in us.”