Challenge 1: A UserForm That Appends a Category — Solution Walkthrough

Private Sub cmdAdd_Click()
    Dim lastRow As Integer
    lastRow = Worksheets("Categories").Cells(Worksheets("Categories").Rows.Count, 1).End(xlUp).Row + 1

    Worksheets("Categories").Cells(lastRow, 1).Value = txtCategory.Text

    Unload Me
End Sub

WHY THIS WORKS AS AN ANSWER
------------------------------
Cells(Worksheets("Categories").Rows.Count, 1).End(xlUp).Row finds the
LAST row that actually contains data in column A of the Categories
sheet — starting from the very bottom of the sheet and jumping
upward until it hits something, the same idiom this course's VBA
Fundamentals chapter introduced. Adding 1 to that row number gives
the first genuinely EMPTY row directly below the existing data,
which is exactly where the new category needs to go.

txtCategory.Text reads whatever text the user typed into the
TextBox — the form's own equivalent of reading a cell's .Value.
Writing that text into Cells(lastRow, 1) on the Categories sheet
appends it as a new row, rather than overwriting an existing entry.

Unload Me closes the form once the category has been added, using
Me to refer to the form itself since this code runs from inside the
form's own module.

Notes:
- Every reference here is fully qualified with Worksheets("Categories")
  explicitly, rather than a bare Cells(...) call — exactly the
  discipline this course's VBA Fundamentals chapter established, so
  this code always affects the Categories sheet specifically,
  regardless of which sheet happens to be active when the button is
  clicked.