If I patented some invention, then who will use it? How are they going to know about this invention. Will the users of this invention pay?
If you apply for a patent on an invention, the documentation for that invention will normally be made publicly available as a US PreGrant Publication. If the invention meets the statutory requirements to be patented (and the appropriate forms are completed and fees are paid), a patent will be granted (and published as a granted US Patent).
Once the patent has been granted on your invention, you will have a limited monopoly on the manufacture, sale, and use of your invention. You can enforce your patent rights (via the civil court system) on infringers and demand compensation and/or cessation of infringing activity.
To your last question: you are not guaranteed a payment from user.
The problem is that enforcing a patent right in the court of law take a lot of time and money, something individual inventors usually don't have. Manufacturers know about this, and some may just take advantage of using your patent without paying.
If you want to monetize on your invention, you may want to first make a prototype, then approach a perspective manufacturer and discuss SELLING your invention without disclosing details of your invention. If someone is willing to buy your invention, you are relieved of subsequent legal burden.
But before that, you may want to consider the following:
- Can the manufacturer easily reverse-engineer your invention through mere look and general discussion?
- Can the manufacturer easily achieve the same result using alternate methods (how crowded is the field, and can you get a very broad patent claim granted that encompasses all alternatives that you can imagine?)