The basic notes of the piano can be found online, a simple google search will show you which notes are which one a piano. The link (bit.ly/i97D4i) shows you how the notes of the piano are named and how they look on a score. It's essential when playing piano to be able to locate middle C. Instructions on how to find middle C can be found here (bit.ly/eIj770).
Once you have got the basics of which notes are which you can then find the music you want. There are many websites which offer free piano music. One example of this is bit.ly/nPq20 (Piano World). You can simply search the song you want and it will search for it. Piano World is very good for modern songs if you want to learn then. However, a more well rounded website is www.sheetzbox.com Also note that blogspot(www.blogspot.com) has many blogs that post music scores to download. The sheet I showed in the next paragraph came from one of these blogs.
The sheet mentioned earlier in the question answers (Miley Cyrus - When I Look at You) can be found here: bit.ly/3lfcA9 It is a scribd file which can be printed off or downloaded easily. Normally to find sheet music it can be as simple as google searching the artists name, followed by the track name followed by "piano sheet."
Another option when trying to find piano music is a trusted music sheet sale company. Somewhere like Music Room (www.musicroom.com) will have both digital copies you can download as well as hard copies you can have sent to you in their stores. However, these are not normally free and will cost you upwards from about £2.50 a score.