Styles and Protection

Using Styles 

The Value column is gray. This is because I applied the Input Style to it. I use the Input style to show where end users can make entries and to unlock input cells. 

Normal Style

In the movie at right, I left clicking on the Normal style, check that protection is part of the style's definition, and its protection tab has Locked checked. This locks all cells set to Normal Style, which is every cell's default style.

Input Style

I then right clicki the input style, make sure protection is part of its definition and uncheck Locked in the protect tab.

Worksheet Protection

With these two styles set, I use option Review > Protect Sheet, uncheck Select locked cells and check Select unlocked cells.