Whereas a slur connects notes of different pitches, a tie is a curved line which connects two notes with the same pitch. They can be of equal length or not. The tie tells you to tongue the first note only, and to hold it for the length of both notes.
Play the G note and hold it for six beats.
A tie may occur either across a bar line, or within one bar. The following example contains ties in bars 3, 5, 6, 7, 8, 11, 13, 14, 15 and 16. Do not confuse the tie with the slur, which connects notes of different pitches.