What does the '+1' sign mean here?
If you mean the "+1" at the end of the curved arrow, that means bend that string upwards one whole step (two frets). Note that you should bend only the string the arrow starts at, not the other string that is fretted. In this example, the G string should be bent but the B string should stay fretted and unbent. If you can read sheet music, the notation above the tab should make it clear.
The notation also shows exactly the timing of the bends. The chord under the "G" should stay unbent for the duration of an 1/8th note and then the A should be bent up. The tiny dot in the A space before the chord after that and the curvature of the arrow indicate a pre-bend. In this case, it means you should keep the string bent from playing the previous chord and pluck the strings again while holding the bend. When this notation follows a rest, it means bend the string during the rest without making any sound and then pluck the strings with the string already bend (hence the term pre-bend).