Protecting Your Art
Prints are delicate and should be handled with care, this means avoiding touching the surface of the print as much as possible, do not store or display your print in humid locations or direct sunlight.
Acid free framing materials, such as an acid free mat and backing will help preserve the print, UV coated plexi is recommended if the art will be placed in a sunny location. 

Borders/Mats & Sizes
Prints are sized to fit most standard frame dimensions (in North America) with no additional borders to avoid having to trim the art, this is helpful when opting for no mat.
If you prefer a mat, premade and custom cut mats are generally cut so that the mat opening is slightly smaller than the print size, this allows for the art to be taped onto the mat. A small portion of the art's edge is usually covered by the mat.

Certificate Of Authenticity
These should be stored in an acid free envelope and can be adhered to the back of your frame for safe keeping, they should also be stored away from humidity and sunlight.

There are many online stores that sell ready-made or custom frames you can assemble yourself, look for acid free mats and backing (mounting board) when purchasing a frame.
If there are local frame shops in your area, it's worth contacting them to get a few quotes.

American Frame - This company provides custom frames that can be assembled at home, it has many positive reviews and frame options that are well priced.