A tie is a curved line which connects two notes with the same position on the staff. 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 melody contains examples of both. Do not confuse the tie with the slur, which connects notes of different pitches.
Here are two examples which make use of everything you have learnt up to this point. To help you develop a good sense of time, try tapping your foot as you play. Also, remember to keep counting regardless of whether you see notes, rests or ties in the written music. There are no breath marks here so you will have to work out the best places to breathe. This shouldn't be difficult, as there are lots of rests in both pieces.