Marquee Left:

Causes Marquee to move Left
Add to <marquee> tag

How to use it:  It is doubtful that you’ll ever need to actually use this as Left is the default direction for a marquee, but just in case, this directs a marquee to travel from the right of the screen to the left.

As I said, you'll likely never need this, but if you're working with a lot of marquees it might be helpful to keep everything straight.

Marquee Right:

Causes Marquee to move Right
Add to <marquee> tag

How to use it:  Similar to the Marquee Left command, this causes the marquee to travel from the left of the screen towards the right.

Marquee Up:

Causes Marquee to move Up
Add to <marquee> tag

How to use it:  This causes a marquee to travel from the bottom towards the top of a window.

Marquee Down:

Causes Marquee to move Down
Add to <marquee> tag

How to use it:  This causes a marquee to travel from the top of a window towards the bottom.

Alternate:

Causes Marquee to alternate
Add to <marquee> tag

How to use it:  This sets the behaviour of a marquee so that it alternates, or "bounces" back and forth within it’s movement path.

Scroll:

Causes Marquee to scroll
Add to <marquee> tag

How to use it:  This sets the behaviour of a marquee to "scroll". That means that the marquee will exit the screen letter by letter when it reaches the edge of it’s movement path. It will then reappear letter by letter back on the other side of the screen.

Slide:

Causes Marquee to slide
Add to <marquee> tag

How to use it:  This sets the behaviour of a marquee to "slide". This means that the marquee will travel towards the edge of it’s movement path, once it reaches it, instead of scrolling off letter by letter as the "scroll" option operates, it instead simply disappears and starts again at the beginning.