In simple terms, a folio is basically a collection of musical pieces sold in a book format.
So if you are not looking for just one song but a collection of songs based on some common theme, then go in for a folio.
Folios may contain a few pieces or several pieces and are usually grouped based on a certain theme, such as songs written by a specific artist or a band or any particular style or the best-selling songs from a particular year.
The layout of the songs in a folio use almost the same format as the pieces available in sheet music. If you do not have any particular song in mind, buying a folio makes sense as it is less expensive than buying separate songs as sheet music.
This is because you can only find the outline or the melody of the musical piece, shown on a treble cleff with chords. You will not find the bass cleff.
This gives pianists a lot of freedom to improvise, since the chords can be played in various ways and can be substituted with other chords.
If you intend to play from a lead sheet, you need to be familiar with chords and should have the ability to improvise. Since only one cleff is printed, most songs in a lead sheet format fit on one page or less.
A lead sheet may or may not provide the lyrics for the song. Similar to folios, lead sheets are also grouped into collections based on some common theme such as style, artist or best-selling year and sold in a book format, called a fake book.
Here's a video showing how to print Music Notation using Recording software
No matter what your skill level is or what sort of music you are looking for, you should be able to find printed music for your needs.
Most of the songs are arranged to suit different levels of skills; popular songs that were not written originally for the piano are taken and arranged so that it can be played on the piano. So you have access to a huge repertoire of songs.
Nowadays, CD-ROMs of written music are also available, which contain a huge collection of songs. Just print the pieces that you like or play it straight form your laptop; and irrespective of whether you are playing from a lead sheet or a sheet music, you can always improvise if you know how to do it.