Function for discreet graph

Hi!

First of all I have never programmed in Excel before. In the attachment you can find my data base and a graph that shows how it shall look later.

I have itemtypes, intimes and outtimes for a storage area. I need the graphs for the content of the storage for each item and the overall content.

Here is the function how I would do it in c++ (I got basic knowledge, I think its not the fastes one but I think it should work). I write a new sheet with data I can generate a graph from. Because I never programmed in Excel I dont know how to do it best.

int totaltime (get from sheet as highest time value or enter manually if much easier)
int r= (function to get amount of rows with values, get from sheet)

int content=0
int a=1 (actual row)
int t=0 (time)

while t smallerorequal totaltime

while a smallerorequal r
int Value2=0
get Value 2 from row a, column2
if Value2=t
content=content+1
int Value3=0
get Value 3 from row a, column3
if Value2=t
content=content-1
a+1
write t and content in Sheet2 in row t+1 and columns 1 and 2

t=t+1


Another proble is that I dont know how to make a dicreet graph in excel. If i make a line I wont have the right graph. Attached you can find a picture how it should look like.

I am thankful for all responses.