yeah its ok, the only way you can start to learn. so basically you could have 3 unbound textboxes on your form. 2 of them would be Y and D, and the 3rd, the result textbox would be X. Name theses textboxes TXTY, TXTX and TXTD. Place a command button on your form, right click the command button, click "build expression" then select "Code Builder".
Place the following code in the area which you're taken to(should be a procedure called "Command1_Click")
if txtY.value = 0 then
TxtX.value = 0
else
txtx.value = txty.value + txtD.value
end if
that will accomplish what you wanted above. let me know how it works.