Start Mixcraft. Click the "Library" tab.
Click on a category in the left-hand column, then drag and drop a loop from the Library onto one of the audio tracks. If you want to add an external loop, double-click inside one of the tracks, navigate to the loop and double-click it.
Click the "View" menu. Hover the mouse over "Snap to Grid" and select "1/64 Note." Drag and drop the loops so that they're adjacent to one another.
Press "Ctrl" and "A" simultaneously to select all of the loops. Click the "Sound" menu and select "Merge to New Clip." Mixcraft combines the loops into one.