Very is a word that intensifies whatever comes after it. When you say something is very hot, you mean it's really, extremely hot. When you describe someone as very tall, you mean noticeably taller than most people.

We use very constantly in everyday speech to dial up the strength of our descriptions. A book might be good, but a very good book is one you can't put down. A problem might be difficult, but a very difficult problem takes serious effort to solve. The difference between “I'm tired” and “I'm very tired” tells people whether you need a snack or a full night's sleep.

Very works with adjectives (descriptive words) and adverbs (words describing actions). You can be very happy or run very quickly. Some writers think that very can make writing weaker rather than stronger. Instead of saying “very big,” you might say enormous or gigantic. Instead of “very tired,” you could say exhausted.

Still, in casual conversation, very serves a useful purpose, helping us express just how much or how intensely we mean something.