Frequently Asked Questions: Patent infringement
A patent document contains a description of the invention (usually with drawings), which explains how the invention can be built and how it works. It also contains a set of "claims". The claims define what the inventor seeks to protect with his patent. So, for something to infringe on a patent, it needs to match the definition given in at least one claim.
For more information, see Determining the scope of a patent.
Patent laws in most countries require some sort of commercial exploitation of the patented invention for the exploitation to be patent infringement. So, a private person can infringe if he, for example, makes the invention and sells it to his friends, or puts it on an advertisement-sponsored website. But if he makes it for himself out of curiosity, and only uses it himself, there is no infringement.
In the USA, also non-commercial use of the invention can be patent infringement, although it is rare for a non-commercial use by a private person to result in a lawsuit.
In practice, the chance of getting sued for patent infringement as a private individual is very slim. Patent lawsuits are very expensive, and most private persons will not be able to pay the damages to the patent holder anyway.