CheckBoxes are very common in Excel forms. Based on the condition whether it is checked or not, you may want to run some code.
Now, how would you check whether the CheckBox is checked or not? It is very simple, use the steps below.

Steps:
1. Open a new file
2. Press Alt+F11 to open VBA editor
3. In the left navigation value select ThisWorkbook
4. In the editor window enter the code below
5. Close the VBA editor
6. Save the file as Macro Enabled File
7. Test with you inputs

Code:
Sub CheckBox()
Dim CheckBox As Shape

Set CheckBox = ActiveSheet.Shapes("Check Box 1") 'Change the CheckBox number you want to check

If CheckBox.OLEFormat.Object.Value = 1 Then
MsgBox "Checkbox is Checked" 'Add your code here which you want to run when CheckBox is checked
Else
MsgBox "Checkbox is not Checked" 'Add your code here which you want to run when CheckBox is not checked
End If

End Sub

CheckBox is Checked

CheckBox is Not Checked

I think this has been informative and I thank you for viewing.

-Saurabh