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 hold it for the length of both notes. Ties are not necessary in Tab notation where you can just follow the count.
Here are some examples demonstrating the use of ties. Count carefully as you play.
Now try this 12 bar Blues in the key of A minor. Remember to keep your strumming pattern going just above the strings whenever you are not actually strumming a chord.