If the words dissolution, solute, solvent, and dissolving don't ring a bell anymore, your can check the basics at Mixtures​. Then, open the Concentration simulation (below on handheld devices, on the right otherwise). It works as follows:

• If you make a mistake, you can reset the simulation by pressing the orange button on the right.
• First, you need to choose the substance to add to water from the Solute dropdown menu. The default is Drink mix.
• Then, place the purple concentration gauge into the solution. In the beginning, it should show 0.000 mol/L.

Now, you are ready to go!