Press the A key, once or twice, so that everything is deselected.
Press the Ctrl button, and hold it down. Hold theLMB down, and drag the cursor around the screen. When you have put the border around the vertices you want to select, release theLMB.
Pres the Ctrl button and the Shift button, and hold them down. Hold down theLMB while you drag the cursor over vertices you have already selected.
You learned to do a lasso selection by holding down the Ctrl button and theLMB, while moving the cursor around the vertices that you want to select. Pressing the Shift button and the Ctrl button, while holding down theLMB, deselects anything within the lasso area.