Here

(near the speaker)

There

(away from the speaker)

Somewhere

(undefined location, usually in positive statements)

Anywhere

(commonly used with negatives and questions)

Everywhere

(all locations)

Examples:

I'm here!

Are you there yet?

That smell is everywhere!

I know I put it somewhere.

I can't find it anywhere.

Are you going anywhere this weekend?

(emphasis on activity)

Are you going somewhere this weekend?

(emphasis on location)

Put that box somewhere in the living room.

(exact location not specified)

Put that box anywhere you'd like.

(at a random location)