how to change color of certain cell in numbers for iPad?

Thank you for the tip on changing color of cells, it worked great.

I am building a spreadsheet with numbers on an iPad, I am partially finished, is there a way to lock the spreadsheet so no one can change it?

When the black, edit button on the upper right side is highlighted, does that mean no changes can be made?

While bouncing around the spreadsheet, I found a lock feature, have not been able to find it again, so what is its purpose and how do I find it.

I have never used this website before but judging from the first answer, I got, it is a fantastic resource. Thanks to anyone who answers my questions.