Hypertonic solution means the solution with a lower water potential than the cell cytoplasm, such as salt water.
When the red blood cell is put into it, since the cell has a higher water potential than the solution, water molecules will flow from the cell back into the water due to osmosis.
Osmosis is always where water molecules flow from a region of higher water potential to lower, through a semi permeable membrane (Whcih is the red blood cell membrane in this case.)
Since water flowed out of the cell, the cell lose water and shrinks.
Hypotonic solution is where the solution that has a higher water potential than the cell cytoplasm.
So when the red blood cell is put in that solution, the water will flow from the solution into the cell this time, by osmosis.
The red blood cell will then gain so much water that the cell membrane cannot hold all and therefore burst.
