Create a VST folder, if you don't already have one. This is the folder where Mixcraft effects plug-ins need to go to be accessed by Mixcraft.
Open Mixcraft, go to the preferences window and click on "Effects."
Click "Edit VST effects." Specify that you want Mixcraft to use VST effects from your newly created folder.
Download GSnap, unstuff the zip file and save it in your VST folder (see Resources for download link).
Restart Mixcraft.
Open the vocal track that you want to autotune. To the left of the track, click the "fx" button. When the fx window opens, click "Select an Effect" and scroll down to "GSnap."
Click "Edit." This will open the GSnap interface.
Click "configure" to select the key that your song is in. You can then control which notes within the scale you want the vocal track to snap to by selecting or deselecting the vertical piano keys on the left side of the interface.