The Time box sets the time signature; the number on the right represents the beat value (whole note: 1, half note: 2, quarter note: 4, etc.), and the number on the left represents how many beats are in one measure. If you are not used to using time signatures, just leave this as 4/4 – that's the most common one.
The Tempo box simply sets how many beats of the song fit one minute; in other words, how fast the song is. The higher this number, the faster the song.
The Grid box does not affect the playback but it only affects the visual representation of the song. By changing the values in this box, you can change the way the grids get drawn on the screen. If you work with short notes, set this to a higher value (e.g., 1/16 and above), if you work with longer notes, set this to a lower value (e.g., 1/4 and lower).