Osmosis is a passive process and happens without any expenditure of energy. It involves the movement of molecules from a region of higher concentration to lower concentration until the concentrations become equal on either side of the membrane.
There are three different types of solutions:
Isotonic Solution is one that has the same concentration of solutes both inside and outside the cell.
Hypertonic solution is one that has a higher solute concentration outside the cell than inside.
Hypotonic solution is one that has a higher solute concentration inside the cell than outside.