"Hincar los codos" y "salir por pies"
Could you please explaine this phrases and give some examples how to use them. Thank you in advance!

Question

Answer

When a person need study a lot, we say "tienes que hincar los codos"

go out running: salir corriendo.

for example. You are in a shop, and you see come an old boyfriend that you do not want to see, you go out of shop quickly.
we say: 
"salí corriendo" (evidently you do not running., you just go out quickly)
también decimos
"salí por pies"

Answer

Hi, "Hincar los codos"= knuckle down or to hit the books, to burn the midnight oil...

The other "to be in a harry to get out of"
Cheers!