The word "lower" can be used as a verb or as an adjective.
As an adjective, "lower" is the comparative form for "low."
Two is a lower number than three.
The air temperature is lower in the winter than in the summer.
The sun is lower in the sky at the end of the day compared to the middle of the day.
The price of gasoline right now is lower than where it was a year ago.
A lower case "L" looks a little like the letter "I."
As a verb, to lower something is to move it down:
Gas stations around the country have lowered their prices recently. (This sentence is in the present perfect tense.)
The United States lowered the minimum voting age from 21 to 18 in the 1970s.
The speed limit was lowered in the 1970s to 55 miles per hour in order to save gasoline and the lives of drivers. Years later, states decided to raise the speed limit back to 65 or 70 miles per hour. (The opposite of "lower" is "raise.")
Some schools lower their standards for admission in order to increase enrollment.
Push down on the audio key to lower the volume on your computer.