So how can someone isolate a sound of an instrument in a song? Let's say I want to do a guitar solo of a song and so I don't want the original guitar solo to be in the song. How can I mute it like others does when they do their guitar solos? How can I mute drums if I wanted to do a drum cover? Same with bass
With an original audio track you can't. There's only two channels, and instruments are mixed across the stereo spectrum in different places, which can't usually be entirely isolated.
Just occasionally, there will be an instrument at extreme left or extreme right, which could then be removed by selecting the other channel. You can usually enhance or reduce certain instruments this way (by panning), but very rarely remove one entirely.

You can get software which will remove anything panned dead centre, by putting the channels out of phase. That usually means removing both lead vocal and bass, because that's normally where those two are mixed. (I use Transcribe for this: it calls that option the "Karaoke" function. It's often useful for learning a guitar part in a song, but won't usually remove the lead guitar.)

Naturally, with a mono track, none of the above will work.

EQ controls can remove certain frequencies, or frequency ranges, but most instruments share ranges anyway. It will work for bass, but at the expense of making the track sound very strange (like it's coming through a phone).

However, you can get backing tracks for various well-known songs, where lead guitar (or something else) has been removed - probably by accessing the original multitrack recording.
You can also get backing tracks which are recreations of originals - covers sounding as close as possible, but leaving out vocals or lead instruments.
Last edited by jongtr at Jul 5, 2016,
The backing tracks on sites like YouTube are not the original tracks from the original recordings, they are new recorded performances from other musicians. Jongtr is correct. You generally cannot remove the instruments from a normal recording.
Yes I am guitarded also, nice to meet you.
Yeah, it's either buy the tracks from the record company or make new ones yourself. The wedding music company I play for has a band that uses backing tracks, and the singer/owner had to make them all himself.

you may be able to find "original" backing tracks for songs on YouTube, but I don't imagine too many are legal enough to stay up.