Sliding is just another technique that gives more interest and life to notes. The idea is that you are going to fret a note (or notes) and then move (slide) to another fret without taking the pressure off your finger (fingers) as you move.

In this example you are fretting the note on the 3rd string, 5th fret and sliding up to the 7th fret. The curved line over top is used to indicate that this is a legato slide. This basically means that you are not going to pluck the note at the 7th fret, you will hear it ring after sliding up to it.

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In this example you are fretting the note on the 3rd string, 7th fret and sliding down to the 7th fret. Again the curved line over top is used to indicate that this is a legato slide.

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Here you are fretting the note on the 3rd string, 5th fret and sliding up to the 7th fret. But because there is not a curved line over the top, you are going to pluck the note at the 7th fret after sliding.

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This is the same as above, only sliding down.

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Here you are sliding up to the 3rd string, 7th fret from an undetermined fret below (usually 2-3 frets). The idea here is that you are not hearing 2 notes, as in the examples above. This is a quick slide, and is hear as one note. The slide is just a decoration of that one note.

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This is the same as above, only sliding down to the 3rd string, 7th fret.

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A glissando, or gliss, uses a longer line. Here you are playing a note, and then sliding up, but not stopping on any particular note. In fact you are releasing the pressure on the string before you stop your left hand. That way you do not hear a stopping point. Just generic slide up. This is used for an effect.

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Here is a gliss down.

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