How can add a song I purchased to my ringtone the instructions say click on song and the click on store but I don't see store?

Which part don't you understand ? On your computer's iTunes :

1, select/highlight the track

2, change its length (Options tab in ‘get-info' ; control-I on a PC, command-I on a Mac) so that its start and end times are at most 30 seconds apart (I think 30 seconds is still the maximum length for a ringtone)

3, create a new AAC version of that shortened track by selecting/highlighting it and doing File > Convert > Create AAC Version (if you have something else instead of 'AAC' go into iTunes' Preferences and change it via the Import Settings button on the General tab)

4, right-click that new track and do 'show in explorer' on the popup (control-click and ’show in finder' if using a mac)

5, delete the new AAC track from the Music part of your iTunes library (not the actual music file, just the entry for it in the Music section of your iTunes)

6, rename the file in windows explorer/finder to have a .M4R extension

See also Create and manage ringtones in iTunes.

tt2

Sounds you are looking at very old instructions. If you've changed your music import settings and the start/end time of the track you now select/highlight the song and use the File > Convert > Create AAC Version menu option