The invention must not be known before you file your application. It does not matter how, by whom or where in the world it has been made known. The invention counts as known even if it is you yourself who has used or published it.
By inventive step, it is meant that the invention must differ significantly from what is already known. The solution must not be obvious to a person skilled in that technical area. That means new ways of combining known methods or objects are not necessarily patentable.
In order to be patentable, an invention must be industrially applicable. An invention is considered industrially applicable if it can be produced or utilized in any kind of industry. "Industry" should be understood in its broadest sense, as including not only what is traditionally meant by “industry” but also other activities, such as transport, agriculture, hunting, public services and medical services.
The requirement of industrial applicability also means that an invention which is clearly infeasible with regard to well-established laws of nature, for example a perpetual motion machine, is not patentable.
There are also exceptions in the patent law to what can be patented, regardless of the three conditions above (novelty, inventive step, industrial applicability) being fulfilled. It is even possible that other authorities might prevent the invention from being used, despite us having granted a patent.