Is
In short
Is is a word used to link a subject to a description or a state of being. It is a form of the verb 'to be' used for singular subjects.
In plain words
It helps you say what something is or how it feels. You use it when talking about one person, place, or thing. It connects the subject to more information.
A simple example
If you say 'The sky is blue', you are using the word to describe the colour of the sky. It links the subject to its quality.
Why it matters
It is one of the most common words in the English language. Without it, you could not make basic sentences to describe the world around you.
Easy to mix up
People often confuse it with 'are', which is used for multiple things instead of just one.