Quick answer
hay = there is / there are; says that something exists, never takes a definite article.
está = is located; says where a specific, known thing is.
Test: if you can put el, la, mi or a name in front of the noun, you need está.
Side by side
Memory trick
Look at the article in front of the noun. <i>un, una, dos, mucho, nada</i> pull hay. <i>el, la, mi, este</i> or a proper name pull está.
Typical mistakes
Hay el supermercado en la calle Mayor.
El supermercado está en la calle Mayor.
Hay never combines with a definite article. Once you say "the supermarket" you are placing a known thing, which is está.
Están muchos turistas aquí.
Hay muchos turistas aquí.
You are reporting that turistas exist in this place, not locating a known group. Quantity words like muchos almost always go with hay.
Check yourself
Fill in: "¿Dónde ___ mi teléfono?"