You can change the direction of the stems using the buttons in the palette.
To add a legato slur, select the range of beats you want to group with a Legato.
Press this button in the palette.
And it will create a legato slur above. Please note that the slur is attached to the staff your cursor was located on when you pressed the key.
You can click on a slur to let the modification handles appear. You can grab these handles and alter the shape of the slur as you want.
To remove a slur, select it with a click and press the Delete key.
To add a grace note, tap this button in the palette.
This will enter in grace note entry mode. You will notice the cursor turned to red.
In grace note mode, the operations will affect the grace note and not the main note it is attached to.
To delete a grace note, simply press Delete when in grace note mode.
You can have multiple independent voices in the same measure. This is simply called multivoice.
Reflow allows you to manage four independent voices.
To change the active voice you're working on, use these buttons in the top left corner of the main window.
All inactive voices will be grayed out, and you can start entering notes on the active voice.