There are 2 main type of guitar slides both of which can be played on one string or multiples:
1: Position Slides = This is where you go from one marked fret to another on the TAB. For example 3/5
2: Glissando Slides = You can slide from wherever you want on the neck as long as you reach the target fret. For example /5
With sliding accuracy is important. When you slide into a note you must end in the middle of the target fret. If you don’t you’ll cut the note short and it won’t ring when you reach it. When you reach the target note keep the pressure down. Use continuous pressure throughout the slide.