A couple of different ways (better ways) to write your question:
Can somebody (or someone) help me with the meaning of this sentence?
Would someone please help to explain the meaning of this sentence?
Russel's answer is correct.
Studies have shown that laughter (laughing) helps to reduce pain and improve health.
So, if you don't laugh, if you don't enjoy your life, and if you aren't happy, then you will feel old.
By the way - you look very young in your photo - too young to be studying any language - nice photo - and it made me smile.