First thing, selling photographs is not easy. A photograph which you may click and like may or may not be liked by someone else.
How long have you been doing photography? The quality of your photographs will wary in accordance with your experience and skill and your photography gear.
Selling photographs can be either for:
A. Commercial purpose (sell them to agencies for marketing, branding, etc)
B. Personal purpose - eg. Wedding Photographers clicks and sells the event photos to his customer who has hired him for the job
C. Editorial purpose - used by news and media agencies
A photograph taken by you - of a bird, plants, flowers, fruits, natural elements, etc (which are not owned by anyone) - are called your own "copyright" photographs. You can go ahead and sell them for commercial use.
Photographs of properties - buildings, shops, homes, etc (which are owned by someone else) would require a "property release" from the owner of the property for you to go ahead and sell those images - even if you have clicked them. If you have a legal release document then you can sell them for commercial use.
Photographs of branded items - cars, mobile phone, shoes, watches, perfume bottles, etc (in which the brand logo is visible) also require a "property release" or appropriate license from the brand manufacturer to sell. (By "brand" I mean - Apple, BMW, Nike, etc). If you have a legal release for this then you can sell them for commercial use.
Photographs of someone else's artwork - like a painting, drawing, sculpture, etc would require a legal release from the artist before you can sell those images.
Photographs of people - weather friends, family or strangers, would require a "model release" - to sell the photos - even if you have photographed them. If you have a legal model release document then you can sell these images for commercial use.
Photos of rail-road tracks, trees, roads, mountain landscapes, public benches, garbage cans, etc. which do not contain other brand elements (like people, cars, prominent buildings, logos) - would not require any license to sell and can be sold for commercial purpose.
Photographing public places - gardens, a Church, A Government Building - like a Court, photographs of public streets with people inside - like shop vendors, children playing, bridges, cars and taxis on streets, street plays, etc (these images can contain brands or buildings or people or all of them) - can be sold using an "editorial license" - These are generally used by news and media agencies and the images can only be used for editorial purpose and not for commercial use.
The difference between such editorial pictures and commercial pictures would mean that editorial pictures cannot be used for commercial purpose - like using them on an advertisement on a Billboard or Hoarding.
To understand licensing and start selling photographs, I suggest you subscribe yourself as a "Contributor" to any of the Stock Photography websites - like Bigstock, Shutterstock, iStock. These websites provide you with very clear licensing and copyright guidelines as to what you can sell, what you cannot and what legal releases would be required.
Check these two links for better understanding:
Click here to start selling your images on Stock and learn a log along the way - this website will not accept bad quality photographs and your rejected photos will make way to better photography - https://submit.shutterstock.com/