Question 1158869
the y-intercept is the value of y when the value of x is equal to 0.


it is helpful to know what specific problems your son is having difficulty with, as the answer to the meaning of the y-intercept depends on the nature of the problem.


the most common usage for young children just starting in algebra is in solving straight line equations.


more specifically, the slope intercept form of the equation of the line is used.


the child is given two points or one point and a slope and the child needs to determine what the equation is.


here's a reference that might be helpful.


<a href = "https://www.purplemath.com/modules/slopyint.htm" target = "_blank">https://www.purplemath.com/modules/slopyint.htm</a>


here's a reference on how to interpret and solve word problems.


<a href = "https://www.purplemath.com/modules/translat.htm" traget = "_blank">https://www.purplemath.com/modules/translat.htm</a>


here's the second page of that reference.


<a href = "https://www.purplemath.com/modules/translat2.htm" target = "_blank">https://www.purplemath.com/modules/translat2.htm</a>


here's some problems that involve the use of the slope intercept form of the equation of a straight line.


<a href = "https://fathersoninnovations.com/wp-content/uploads/2018/06/Slope-Intercept-Form-Word-Problems.pdf" traget = "_blank">https://fathersoninnovations.com/wp-content/uploads/2018/06/Slope-Intercept-Form-Word-Problems.pdf</a>


here's a tutorial on how to derive the slope intercept form of the equation of a straight line.


<a href = "https://www.mathsisfun.com/equation_of_line.html" target = "_blank">https://www.mathsisfun.com/equation_of_line.html</a>


here's another reference on how to find the equation of a straight line, given certain attributes of the line.


<a href = "https://www.purplemath.com/modules/strtlneq.htm" target = "_blank">https://www.purplemath.com/modules/strtlneq.htm</a>


your question is very general.
it helps to understand the question in terms of the specific problem your son is dealing with.


going through a couple of examples can help to determine how the y-intercept is used to solve those problems.


web searches such as i did to find some references can also be helpful.


youtube also has lots of tutorials that can also be helpful.