No pain no gain.

No pain no gain. - Sin esfuerzo no hay ganancia.

This is an idiom that means if you don't make an effort in doing something, you can't achieve your goals.

Tighten someone's belt

Tighten someone's belt - Apretarse el cinturón.

Not having enough money to spend.

I've lost my job because of the crisis, now I have to tighten my belt. - He perdido mi trabajo por la crisis, ahora tengo que apretarme el cinturón.

Hacer bolas / pelotas

Hacer pelotas, hacer bolas , enredarse = not comprehend something clearly, get confused.

Example:

Estaba escribiendo en el blog pero me hice pelotas. - I was writing on the blog but I got confused.

Juan se hizo bolas con el problema de matemáticas y no lo pudo terminar. - John didn't comprehend well the math's problem and he couldn't finish it.