You can earn some money stuffing envelopes but be aware that it's just a pyramid scheme. I'm not saying all of them are a scam but some could be.
Do your research before signing up for a stuffing envelope company job.
The way the envelope stuffing works is you signup with the envelope stuffing company and pay a fee from $36.00 to $70.00 depending on the company.
The envelope stuffing company then sends you an envelope stuffing kit, this kit will contain a flyer that you copy and then stuff into other envelopes and mail to other people on a list that should come with the envelope stuffing kit.
This flyer that you mail tells other people how they too can make money stuffing envelopes. If people decide to signup for the program then you will receive a small commission of around $5.00 per signup.
You can make some money doing so but you won't get rich doing it.