Something that exists is there. So we use 'There is' to say that one thing (singular) exists, and 'There are' to say that two or more things (plural) exist.
Use 'There is' when you want to talk about one thing (singular). The contracted form is 'There's.'
There's an egg in the fridge.
There are + two or more things
Use 'There are' when you want to talk about two or more things (plural).
There are eggs in the fridge.
You can leave out the name of the place ('in the fridge') when it is clear from the context: "There's an egg!" / "There are eggs!"
Why does 'There is' become 'There are'?
You may wonder why 'There is' becomes 'There are'. The reason is that the subject of the sentence is 'egg ' or 'eggs ' and not 'There'.
