do you know what diffusion is?
gas molecules diffuse from an area where there is a high concentration of the gas to a low concentration (down a concentration gradient)
osmosis is diffusion of water molecules - that's all
also osmosis happens across a membrane: partially permeable membrane because the water molecules need to be able to pass through so it has to be partially permeable otherwise nothing would be able to cross it.
an example: imagine the inside and outside of a cell. the plasma membrane of the cell counts as the partially permeable membrane - water moves across this membrane - if there is more water outside of the cell then water will move into the cell "by osmosis" and if there is more water inside of the cell water will move out of the cell "by osmosis"
(water does this to try and balance out the amount of water on either side of the membrane)
the kind of questions you're likely to be asked that I can think of atm
(a) define osmosis
(b) hypertonic, hypotonic, isotonic solutions
(c) whether osmosis is active or passive
(d) random visking tubing experiment