My understanding is that hydrostatic pressure is the pushing power of circulating blood and fluid. ie, Fluid pushes itself through the normal "leaks" in the small spaces between the thin cells of the capillary walls. Then the fluid goes into the tissues, cells, etc. outside of the capillaries. This is hydrostatic pressure.
Colloid osmotic pressure is just the opposite, and it is exerted by the protein albumin. Albumin is normally too large to pass through the capillary walls, so it stays inside the capillaries. The structure of albumin is such that it pulls fluid towards itself. (How and why it does this is probably beyond my own ability to understand or explain, but just know that it does this. lol.) This effect of albumin is colloid osmotic pressure. This keeps too much fluid from leaving the capillaries.
The simplified version
is that hydrostatic pressure pushes fluid out of the capillaries, while colloid osmotic pressure keeps fluid inside the capillaries.
There's a good visual about this in one of my books. Wish I could show it to you, esp since I had a problem understanding this myself one time.
Anyway, hope this helps!