In traditional notation, a tie is a curved line that connects two notes with the same position on the staff. A tie indicates that you play the first note only, and to hold it for the length of both notes.
A tie is not necessary in Tab notation where you can just follow the count. The use of ties is another common way of creating syncopated rhythms.
The following example demonstrates the use of ties both within a bar and across bar lines. The use of a tie is the only way of indicating that a note is to be held across a bar line. Do not confuse the tie with the slur, e.g. hammer-on, pull-off, bend or release, which connects two notes of different positions on the staff.