Why is there a chord notation above some measures of a song's tab notation?  Would you play the chord?  Would you play the chord?

 

Here is an example for GnR's version of "Knockin On Heaven's Door"

http://tabs.ultimate-guitar.com/g/guns_n_roses/knockin_on_heavens_door_tab.htm

 

Above the first measure I kinda understand the G5 to start off the song as that is the notes being played, half way through the measure it shows a "D" chord but when and why would you play it or would you play it?  If not then why is it there?

 

Moving to the second measure there is a "C" chord shown but again I see nowhere you would play the chord.  Is this for a second guitar to be playing along?

 

Sorry for the rookie question, but I've been wondering about this for a while.

First of all, don't apologise. It's all about learning :)

 

The short answer is, you wouldn't play it. 

 

Look closely though. That 0-2-3-2 note part where it shows you the D symbol...does that look familiar? It should, because those 4 notes there are your D chord! It's basically a finger placement guide.

 

So, instead of having to quickly move your fingers from 0 to 2 to 3 etc, if you just make a d chord shape, your fingers will already be in the right place.

 

You'll see this sort of thing shown quite a lot during playtime on Rocksmith too. Hope this clears it up a little :)

Thank you immensely! 

Any time, friend.

 

That's what this place is for!

To amend Dale's answer a bit, and give you credit for guessing right (about the second guitar part)

 

edited to lead with a TL:DR, -> They indicate chord changes in a song.

If you're bored, keep reading...

A rhythm guitarist/bassist/ukulele/harmonica player/pianist could "fake" an arrangement using those chord changes.

Some things to keep in mind, are that rhythm guitarists probably wouldn't just play a single strummed chord when they see D, or Dmin, or D7, etc (<- different chord shapes), they would usually play multiple strums with the beat of the song.

Bass players might play the single notes indicated, might play arpeggios using that note as a "base" note ie, they'd play something like D - then F# - then A - then the F# - D or whatever sounds most rhythmic. (or they could play power chords or double stops ie: D on the A string and D on the G string at the same time, etc)

With the ukulele, and many other instruments, you can play a chord-melody arrangement. Often that means a chorded strum on the change, followed by playing some cool sounding individual notes from the melody of the song. (like in combo mode from RS1) (Also, ukulele players often travel in large packs, so trying to get everyone to "meet up" at chord changes is a good way to keep in time if you don't have drums or bass to help with that.

Then you get those @!#$!%ers on piano who can play chords with the left hand while simultaneously playing melody with the right... (yes, I'm jealous)