Hi!
Josh was blowing bubbles through a straw into a glass of tap water. As Josh exhaled into the straw, he blew carbon dioxide gas into the water. The harder he blew, the more bubbles entered the water. The more bubbles, the more concentrated the solution gas/water
A solution is a mixture of a solute (A substance that is dissolved and is in the least amount, in this case, the CO₂) and a solvent (The substance that is dissolving the solute, in this case, the water). When blowing bubbles into the water, Josh is adding more CO₂ (Solute) to the mixture, making the concentration of the gas in the water to rise up, as the amount of solute will be higher.
Have a nice day!