A saturated solution is one in which the solvent (water) has achieved equilibrium between the dissolved and undissolved solvent. What does that mean? The water has absorbed all of the chemical which it can hold.
The hotter the water the more chemical it can hold. So what we're going to do is heat up the water (I suggest 100 degrees but substantially above room temperature will do boiling is definitely not necessary ). I found that tap water did not stay hot long enough and it was necessary to use a pan and the stove.
Pour about 500-700 mL of water into a pan, basically you want enough to fill your bottle with a reasonable margin of error (I used about 1 1/2 bottles). If you're a purist or doing real chemistry distilled water can be used, otherwise tap water will probably be fine. Soft water should be avoided as it already has dissolved salts (of a different type) and this may impact the proposed use.
Once the water has heated up add some salt and stir until fully dissolved. If you use a kitchen scale measure you can measure out about 100g as a starting point otherwise just pour some in and stir. Repeat this until the salt no longer dissolves and wet salt crystals appear on the bottom of the pan (see picture). There is no particular danger in adding too much but no need to overdo it.
Remove the pan from the heat and allow to cool to room temperature. Some folks filter the solution, I was able to carefully pour off 500 mL of solution into a measuring cup without getting any surplus salt. Then carefully pour that into one of the bottles. Close the bottle and label it "Master Solution" or "Saturated Solution". Actually I marked mine "Saturated Saline" since I frequently have more than one type of solution on hand.
The next step will talk briefly about the solubility of various household chemicals such as lye ( Sodium Hydroxide ) or Epsom salts and then we'll look at making solutions of various strengths.