Prima volta means first time. It is one of the common shorthand-notations in music.
The sequence played in the above example will be : G, G#, G, A
The second time (after hitting the repeat-bar line) the prima-volta part is skipped and the secunda_volta part is to be played.
Please note that in this example the repeat-dots in the first bar are omitted (as is common practice).
See also dal segno