Connect your MIDI keyboard to your computer. Many MIDI keyboards connect directly to the computer via USB. However, although most sound cards have virtual MIDI interface capabilities, some do not. In this case, you will need an external MIDI interface. Using a standard MIDI cable, connect the "MIDI Out" port on the keyboard to the "MIDI In" port on the interface. Connect the interface to the computer via USB. Turn on both the interface and keyboard once connected.
Open Mixcraft. Once it has loaded, click the button labeled "+ Track" in the upper left. A drop-down menu will appear. Select "Insert Virtual Instrument Track." A new virtual instrument track will appear in Mixcraft's arrangement area.
Check that Mixcraft will receive MIDI input from your MIDI keyboard. Mixcraft is designed to use any connected MIDI keyboard by default, but occasionally will default to an incorrect MIDI port. In the menu bar, click "File" and select "Preferences." A settings dialogue will appear. Click on the "MIDI" tab. Find your keyboard and the port listed here. Select it and click "OK."
Select a virtual instrument by clicking on the keyboard icon on the virtual instrument track. A dual-paned dialogue box will appear in which the different plug-in categories are listed on the left and the instruments and effects that fall under the selected category are listed on the right.
Select "VSTi Instruments" in the left pane. All installed VST instruments will appear in the right pane. Double-click on the name of the instrument you want to play. Mixcraft will load the instrument on the virtual instrument track and its interface will appear.
Play your MIDI keyboard. Mixcraft will route the the MIDI data sent by your keyboard into the virtual instrument, making it play back your performance.