There are two ways. Use a new layer, or use a voice. I hate voices, though some users swear by them, so I will tell you the layer method.

Enter the music for layer 1, including all the material that has to be on stems-up layers, as well as what is at the beginning of the measure.

Go to Layer 2, enter a rest, hide the rest (in Speedy Entry that's the O key) and enter the stem-down music. It will appear that Layer 2 starts after the hidden rest.

You may have to manually flip stems in the first part of the measure.

Great. Thanks very much!

Hi how do you flip the stems? I am using Finale printmusic 2014 for a Mac.

Choose the note in Speedy Entry and press the L-key.

You can also use the Document options to specify stem direction for an entire layer.

(How many times do you have to ask the same question?)