You can hear the sample sound by clicking on its name in the instrument panel. You can also hear the sound of every hit by clicking it while in the Play mode or right-clicking and selecting Play, when in Standard mode.
You can easily add new tempo by holding down Ctrl and clicking on the tempo panel. (above the bar numbers)
You can move tempo by holding down Shift and dragging the tempo to a new position.
You can use many keyboard shortcuts (hotkeys) to make your life easier with Drumsite. For example, you can start and stop playing by using Space key. Check Help for the full list of hotkeys.
You can assign individual samples or sample groups to a key and practice playing like a real drummer! You can also record what you play, by clicking Record button when you start and again when you are finished with drumming. Note that hits appear only AFTER the recording is finished. You can also record while Drumsite is playing already existing rhythm.
You can use Volume mode to adjust hit volumes easily. Right-click group or sample name and select Volume mode. Then click or drag with mouse button to change volumes for one or multiple hits. Watch tutorials for demonstration. With this function you can create fade-in or fade-out in a second!
You can use Panning mode to adjust hit volumes easily. Right-click group or sample name and select Volume mode. Then click or drag with mouse button to change volumes for one or multiple hits. Watch tutorials for demonstration.
You can easily compute new tempo value when changing time signatures by using Beat change calculator. (menu Tools | Beat change calculator) For a demonstration of changing time signatures, open the "Same rhythm different tempos" demo.
A group of hits can easily be selected by dragging a selection rectangle - holding down CTRL key and left-clicking the upper left corner of the selection area and dragging the cursor to the desired direction. 
By pressing CTRL + T over the bar - all hits in bar will be selected or deselected.
Hit modes can be very useful in case you want to play with dynamics of the instrument. Every sample has assigned its hit mode and this is evaluated when adding hits - only the samples with the corresponding hit mode set are used. Hit modes for sample are set in the drumset editor.
You can use Pattern manager, a tree-structured list of drum patterns you can quickly glue together to create a song. Press Alt+E to invoke pattern manager.
When exporting your song to WAV format, you can set custom output sample rate (44100 Hz is default) and number of loops.
When you have performed some undesired operation, you can use unlimited Undo (Ctrl+Z) and Redo (Shift+Ctrl+Z) functions.
There are many demo songs with Drumsite, you can use these for your inspiration and for better understanding how various rhythms work.
You can use multiselection and drag&&drop operations to organize things in Pattern Manager.
You can use multiselection and drag&&drop operations to organize things in Drumset editor.
You can use Ctrl+D key combination to quickly clear any selection.
Every sample is intialized before it is played for the first time. This takes a little time, but the delay may be disturbing when trying to play your own tempo with keyboard. To avoid this, either "train" all samples you would like to use or press Initialize all samples button on the toolbar.
You can quickly save selected hits as a pattern, by pressing Ctrl+P which invokes the save dialog. Saved pattern, which is in the same format as standard Drumsite song, can then be added to Pattern manager tree.
When using Pattern Manager patterns, they are either inserted to the first available position or to the mouse position. You can set this behaviour in Options | Insert pattern from mouse position menu.
You can use shortcuts to quickly change the number of dividings for bars. Try Alt+8, Alt+6, Alt+4 etc.
You can see the starting time for each bar at the foot of the Drumsite window.
Every hit may have its custom fade-off that can be selected in hit's properties. Right-click the hit, select Properties from the popup menu and set desired End time.
You can set many effects for your samples in Drumset editor. (reverb, equalizer, distortion, gargle, compressor etc.) You can also change pitch of the samples.
You can use multiselection in Drumset editor and apply settings to multiple items in one operation.
You can use your own WAV, MP3 and OGG Vorbis samples in Drumset editor, any samplerate, mono or stereo.
You can set custom cut-off map for a group or sample in Drumset editor. This means that pedal hi-hat for instance is cutting of hi-hat sound or bass sample on one string fades off with other bass sample on the same string.