Cells
Entering and editing data
A cell holds one of three things: a number, text, or a formula (starting with =). Learn the difference between typing in the cell and typing in the formula bar, and how to edit with F2 or a double-click. Understand that pressing Enter confirms and usually moves down, while Tab confirms and moves right. A key trap: text that looks like a number (for example a leading apostrophe) is stored as text and will not calculate.
Copying, moving and filling
Use Copy/Paste and Cut/Paste, and know the fill handle for copying patterns and series. The critical distinction is relative vs absolute references: a relative reference (A1) adjusts when copied; an absolute reference ($A$1) does not; mixed references lock only the row or column. Questions often ask what a formula becomes after copying - trace each reference.
Inserting, deleting and clearing
Know the difference between Delete (removes contents, keeps the cell) and Delete cells/rows/columns (removes the cell and shifts others). Clear can remove contents, formats, or both. Traps include assuming deleting a row only clears values, and forgetting that deleting cells shifts references.
Sorting and finding data
Use Find/Replace to locate or change entries, and Sort to order data ascending or descending. Remember that sorting rearranges whole rows, and that a sort on numbers stored as text follows text order (so "10" may come before "9").
Worked example
In B1 you have =A12. Copy it to B2. Because A1 is relative, it becomes =A12 in B2 only if the reference moved one row - actually it becomes =A22. If you needed A1 fixed, you would write =$A$12.