Dropdowns, and dropdowns that depend on each other

Every SUMIFS and COUNTIFS you write matches text exactly. If one person types Closed Won, another Won and a third Closed - Won, your pipeline report has three stages where there should be one. The fix is to stop people typing: give them a dropdown.

1. Select the cells people will fill in, say the Stage column C2:C500.
2. Data › Data validation › Add rule.
3. Under Criteria, choose Dropdown and type the options: Discovery, Proposal, Negotiation, Closed Won, Closed Lost. Give each one a color if it helps.
4. Under Advanced options, set If the data is invalid to Reject the input, so nothing else gets in.

If the list changes often, choose Dropdown (from a range) instead and point it at a list on a Lists tab. Add an option there and every dropdown picks it up. Insert › Dropdown is a shortcut to the same panel.

Dependent dropdowns are two dropdowns where the second one's options depend on the first. Pick Channel = Social, and the Campaign dropdown offers only social campaigns. Sheets has no single setting for this, but a helper range does it:

1. On the Lists tab, give each channel its own column: the channel name in row 1 (Search, Social, Email in A1:C1) and its campaigns underneath.
2. On the Form tab, make B2 a dropdown from the range Lists!A1:C1.
3. In an empty spot on Lists, say E2, return the column that matches the chosen channel: =INDEX(Lists!A2:C20, 0, MATCH(Form!B2, Lists!A1:C1, 0)). A row of 0 means the whole column.
4. Make Form!C2 a dropdown from the range Lists!E2:E20.

Change the channel and the campaign list follows. This works well for one input cell, like a form or a dashboard filter. If every row of a long log needs its own dependent dropdown, you need a helper for every row, and many teams settle for one dropdown of combined values like Social: Spring Promo instead.